Safety, waste management and quality control

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This section covers the types of hazard found in chemical industries, including those due to high pressure and explosions, dust and vapour cloud explosions, vacuum and temperature, inflammable and toxic materials, hazardous chemicals, reactions and operations, electrostatics and ionizing radiation, noise hazards and their effects on personnel and plant operation, and fire and explosion indices and hazard analysis.

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Hazard, Risk and the Control Hierarchy • A hazard is anything with the potential to cause harm; risk is the combination of the likelihood that the harm will occur and the severity of its consequences.

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A hazard cannot be removed by a procedure — only by eliminating or substituting the substance or the operation — whereas risk can be reduced by lowering either likelihood or severity. • The hierarchy of control, in strict order of preference: • 1.

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Elimination — remove the hazard entirely; the only completely reliable measure. • 2.

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Substitution — replace with something less hazardous. • 3.

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Engineering controls — containment, ventilation, interlocks, relief systems; these protect everyone without depending on behaviour. • 4.

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Administrative controls — procedures, permits to work, training, signs, job rotation. • 5.

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Personal protective equipment — the last line of defence, protecting only the wearer, and only if it is correctly selected, fitted, worn and maintained. • Inherently safer design is the modern expression of the top of this hierarchy, and its four principles should be known: minimise (use smaller inventories of hazardous material), substitute (use a less hazardous material or route), moderate (use less severe conditions or dilute forms) and simplify (design out the complexity that causes error).

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The guiding maxim is that what you do not have cannot leak.

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Fire and Flammability • The fire triangle requires fuel, oxygen (oxidiser) and an ignition source; the fire tetrahedron adds the chemical chain reaction, which is what halon and dry powder extinguishers interrupt.

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Removing any one leg extinguishes the fire, and the three classical methods — starvation, smothering and cooling — correspond to removing fuel, oxygen and heat respectively. • The temperature definitions must be known exactly: • Flash point — the lowest temperature at which a liquid gives off sufficient vapour to form an ignitable mixture that flashes momentarily on application of a flame.

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It is the single most important property for classifying a flammable liquid. • Fire point — a few degrees above the flash point, at which burning continues once started. • Autoignition temperature — the temperature at which the material ignites spontaneously with no external ignition source; it is much higher than the flash point. • Flammability (explosive) limits: a vapour-air mixture burns only between the lower flammable limit (LFL) and the upper flammable limit (UFL).

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Below the LFL the mixture is too lean and above the UFL too rich.

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Widening limits and a low LFL mean a more dangerous material — hydrogen and acetylene have famously wide ranges. • Inerting with nitrogen reduces the oxygen below the limiting oxygen concentration, at which combustion cannot occur whatever the fuel concentration; it is the standard protection for storage tanks and reactors. • Fire classes:

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A ordinary combustibles, B flammable liquids, C flammable gases, D combustible metals, and electrical fires, with class F or K for cooking oils.

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Water must never be used on burning oil (it spreads the fire by boiling violently beneath it), on live electrical equipment or on reactive metals.

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Explosions Event Description Typical cause Deflagration Combustion front travels below the speed of sound in the unburnt gas Most ordinary vapour and dust explosions Detonation Front travels above the speed of sound, producing a shock wave and far greater damage Confined explosions, sensitive materials, deflagration-to-detonation transition in long pipes Confined vapour cloud explosion Ignition inside a vessel or building; pressure rises rapidly with nowhere to vent Leak into an enclosure Unconfined vapour cloud explosion (UVCE) A large release forms a drifting cloud that ignites in the open, producing blast overpressure Major loss of containment of a flashing liquid or gas Flash fire The same cloud burns without significant overpressure Smaller release or low congestion BLEVE Boiling liquid expanding vapour explosion: a vessel of liquid above its atmospheric boiling point fails, the contents flash instantly and, if flammable, form a fireball Fire impingement on the vapour space of an LPG vessel, weakening the shell Dust explosion Suspended combustible dust ignites; often a small primary blast raises settled dust and triggers a far larger secondary explosion Grain, flour, sugar, coal, metal powders, plastics, pharmaceuticals Runaway reaction Heat generation outruns heat removal and the reaction accelerates uncontrollably Loss of cooling, wrong charging, contamination, agitator failure • The dust explosion pentagon adds dispersion in a cloud and confinement to the three legs of the fire triangle.

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The secondary explosion is usually far more destructive than the primary, which is why good housekeeping — preventing dust accumulation on ledges and beams — is the single most effective control.

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A finer dust is more dangerous, because its surface area per unit mass is greater. • A BLEVE is a physical explosion first and a fireball second; it can occur with any liquid held above its atmospheric boiling point, flammable or not.

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Protection is by water cooling of the vessel shell, fireproof insulation, and adequate separation distances. • Pressure hazards: over-pressurisation from blocked outlets, thermal expansion of trapped liquid, external fire, utility failure or runaway reaction is guarded by relief valves and bursting discs discharging to a safe place.

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Vacuum is equally dangerous and is more often overlooked: a tank that is drained or steam-cleaned and then cooled without an adequate vacuum breaker will collapse, and vessels are far weaker in vacuum than in pressure — a favourite examination point. • Temperature hazards include thermal stress, loss of strength at high temperature, and brittle fracture at low temperature, where a steel that is ductile at ambient becomes brittle below its transition temperature — relevant wherever cryogenic or auto-refrigerating fluids are handled.

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Toxic, Electrostatic and Radiation Hazards • Routes of entry are inhalation (the principal industrial route), skin absorption and contact, ingestion, and injection through a wound. • Exposure limits:

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TLV-TWA is the time-weighted average for an eight-hour day and forty-hour week;

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TLV-STEL is a fifteen-minute short-term limit;

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TLV-C is a ceiling that must never be exceeded even momentarily; and IDLH is the concentration immediately dangerous to life or health.

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LD₅₀ and LC₅₀ are the dose and concentration lethal to half a test population — a lower value therefore means a more toxic substance, which is regularly inverted by mistake. • Acute effects appear rapidly after a single exposure; chronic effects develop slowly after repeated exposure at levels too low to cause acute symptoms, and include carcinogenic, mutagenic and teratogenic effects.

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Asphyxiants are divided into simple (displacing oxygen, such as nitrogen and carbon dioxide) and chemical (interfering with oxygen transport or use, such as carbon monoxide and hydrogen cyanide).

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Nitrogen asphyxiation in confined spaces is one of the commonest causes of industrial fatality precisely because nitrogen gives no warning at all. • The Safety Data Sheet (SDS), in its sixteen-section format, is the primary source of hazard information, and the Globally Harmonized System (GHS) standardises classification, pictograms and the signal words Danger and Warning. • Electrostatic hazards arise wherever a non-conducting liquid flows through a pipe, is splash-filled into a tank, or a powder is pneumatically conveyed or poured.

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The charge accumulates and discharges as a spark of enough energy to ignite a flammable atmosphere — and the minimum ignition energy of a vapour is only a fraction of a millijoule, far below what a person can feel.

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Control is by bonding and earthing all conductive equipment, limiting fill velocity, bottom filling rather than splash filling, using antistatic additives, and inerting.

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Note that earthing protects only conductive items; a plastic container or a non-conductive liquid cannot be earthed, which is why plastic containers are prohibited for flammable liquids. • Ionizing radiation from level and density gauges, thickness gauges and radiography is controlled on the three principles of time, distance and shielding, with distance following an inverse square law; sources are licensed, interlocked and monitored with film badges or dosimeters. • Noise hazards: prolonged exposure causes permanent, irreversible noise-induced hearing loss, which develops painlessly and is not noticed until it is well advanced; it also causes tinnitus, stress, fatigue and raised blood pressure.

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Operationally it masks alarms and speech, interferes with communication, and so becomes a cause of accidents in its own right.

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The usual industrial criterion is about 85-90 dBA for an eight-hour day, with the permissible exposure time halving for each 3 dB (or in some systems 5 dB) increase — the exact exchange rate depends on the national regulation, which must be checked.

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Control follows the hierarchy: quieter equipment, enclosure and silencers, then limiting exposure time, and hearing protection last.

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Hazard Analysis Techniques Technique Nature Use HAZOP Systematic, team based, applied line by line with guide words (no, more, less, as well as, part of, reverse, other than) against design intent The standard qualitative study for a complete process; thorough but time consuming What-if / checklist Structured brainstorming against experience Quick screening; simpler processes; early design FMEA Failure mode and effects analysis, component by component, often ranked by a risk priority number Equipment and control system reliability Fault tree analysis Deductive: starts from a defined top event and works down to root causes; quantifiable Determining the probability of a specific accident Event tree analysis Inductive: starts from an initiating event and traces forward through success and failure of each safeguard Assessing the range of possible outcomes Bow-tie Combines a fault tree and an event tree about a central loss-of-containment event Communicating barriers to management and operators LOPA Layer of protection analysis: semi-quantitative check that enough independent layers exist Deciding the required safety integrity level Dow F&EI;

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Fire and explosion index: a numerical score from material factor and penalties for general and special process hazards Ranking units by relative hazard and setting the radius of exposure • HAZOP is the technique most often named in examinations, and its distinguishing features are that it is carried out by a multidisciplinary team, applied systematically node by node, and driven by guide words combined with process parameters to generate deviations from the design intent. • The Dow Fire and Explosion Index starts from a material factor based on flammability and reactivity, applies penalties for general process hazards (exothermic reaction, material handling, enclosure, drainage) and special process hazards (operation within the flammable range, toxic materials, pressure, quantity, corrosion, leakage), and yields an index that is translated into a degree of hazard and a radius of exposure.

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The Mond index extends it to include toxicity.

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This section covers occupational health and safety management and safety culture, the storage of dangerous materials, safety protection and equipment for personnel and plant against various hazards, safety procedures, disaster management, insurance, and workers' safety legislation.

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Safety Management Systems and Culture • A safety management system follows the Plan-Do-Check-Act cycle, the same structure used by ISO 45001 for occupational health and safety and ISO 14001 for environmental management, which is why an organisation can integrate them.

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ISO 45001 replaced the earlier OHSAS 18001. • Its elements: policy and leadership commitment, hazard identification and risk assessment, legal compliance, objectives and planning, competence and training, communication and worker participation, operational control, emergency preparedness, performance monitoring, incident investigation, internal audit, and management review. • Safety culture is the shared values, attitudes and behaviours that determine how safety is actually treated when no one is watching.

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Its hallmarks are visible leadership commitment, worker involvement, open reporting without blame, learning from incidents and near misses, and the authority for anyone to stop unsafe work.

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A mature culture treats a near miss as a free lesson and investigates it as thoroughly as an injury. • The accident triangle (Heinrich) holds that for every serious injury there are many minor injuries and a far greater number of near misses and unsafe acts.

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The practical conclusion — which is what the examination asks — is that acting on the broad base of near misses is the way to prevent the rare event at the top. • Key measures: lagging indicators such as the lost-time injury frequency rate and severity rate record what has already gone wrong; leading indicators such as near-miss reporting, audit findings closed and training completed predict future performance.

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Relying on lagging indicators alone is a recognised weakness, because a low injury rate can coexist with a high risk of a major accident — the central lesson of several major disasters. • Process safety is not the same as occupational safety: slips, trips and cuts are occupational; loss of containment, fire, explosion and runaway reaction are process safety, and good personal-injury statistics say nothing about process safety performance.

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Storage of Dangerous Materials • Segregation by compatibility is the governing principle.

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Oxidising agents must be stored away from flammables and organics; acids away from bases and from cyanides and sulphides, which would release hydrogen cyanide and hydrogen sulphide; water-reactive materials away from any source of moisture; and peroxides and other unstable materials in cool, dark, dedicated storage. • Flammable liquid storage requires bunding (secondary containment) of at least the capacity of the largest tank plus a freeboard allowance, adequate separation distances, earthing and bonding, flame arresters and conservation vents, nitrogen blanketing for the more volatile liquids, fixed foam or water spray systems, and the exclusion of ignition sources through hazardous-area electrical classification. • Pressurised and liquefied gases are stored with relief protection, water deluge for fire exposure, fire-resistant insulation, and generous separation distances, because of the BLEVE risk.

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Cylinders are stored upright and secured, with valve caps fitted, in ventilated areas, and full and empty cylinders segregated. • Good practice for all storage: minimise inventory (the first principle of inherently safer design), label everything clearly to GHS, keep the SDS accessible, provide adequate ventilation, control temperature, inspect regularly, and rotate stock so that unstable materials do not exceed their shelf life.

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Protective Equipment and Safety Procedures Category Examples Notes Head, eye and face Helmet, safety spectacles, goggles, face shield Goggles for splash and dust; face shield in addition, never instead Respiratory Dust mask, half and full face respirators with cartridges, air-line and self-contained breathing apparatus A filtering respirator is useless in oxygen deficiency or an unknown atmosphere; only air-supplied apparatus will do Hand and body Chemical-resistant gloves, aprons, chemical suits Glove material must be matched to the chemical; breakthrough time matters as much as resistance Hearing Ear plugs, ear muffs Selected by attenuation rating against the measured noise level Fall protection Harness, lanyard, anchor points For work at height and in confined spaces Foot Safety shoes with toe cap, chemical and antistatic soles Antistatic footwear is required where flammable atmospheres may occur • Plant protective systems include pressure relief valves and bursting discs, flare and vent systems, emergency shutdown systems, fire and gas detection, fixed firefighting systems, blast walls and containment bunds, and safety instrumented systems designed to a defined safety integrity level.

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The protective layer must be independent of the basic process control system, so that a single failure cannot disable both — the point already made in Chapter 8. • Essential safety procedures, each of which may be named in a question: • Permit to work — a formal written authorisation for non-routine or hazardous work, specifying the precautions taken and the limits of the job, issued and signed off by a competent authorising person. • Lockout-tagout (LOTO) / isolation — physically isolating and locking off every energy source before maintenance, with each worker applying a personal lock.

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Energy includes not only electricity but pressure, stored mechanical energy, gravity, heat and chemical energy. • Confined space entry — the highest-risk routine activity in a plant.

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It requires isolation and cleaning, atmospheric testing for oxygen, flammables and toxics before and during entry, forced ventilation, a permit, a trained attendant stationed outside, harness and rescue equipment, and a rehearsed rescue plan.

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Most confined-space fatalities are would-be rescuers who enter without breathing apparatus, which is why unplanned rescue entry must never be attempted. • Hot work permit — for welding, cutting and grinding in areas where flammables may be present, with gas testing, removal of combustibles and a fire watch maintained after work ends. • Management of change — any change to plant, process, materials, software or organisation must be formally reviewed, because unreviewed change is one of the commonest underlying causes of major accidents. • Incident investigation — the object is to identify root causes and system failures, not to apportion blame, since a blame-seeking investigation destroys the reporting it depends on.

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Disaster Management, Insurance and Legislation • The disaster management cycle runs mitigation (reducing the hazard and vulnerability before anything happens) → preparedness (plans, training, drills, resources) → response (the emergency itself) → recovery (restoration and rebuilding).

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Mitigation and preparedness occur before the event and response and recovery after it — a sequence commonly asked for. • An on-site emergency plan covers events contained within the plant boundary; an off-site emergency plan, prepared with the local authority, covers events that affect the surrounding population.

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Both require defined roles, an emergency control centre, alarm and communication arrangements, assembly points and headcounts, evacuation routes, medical and mutual-aid arrangements, and regular drills. • Insurance transfers financial risk but does not reduce physical risk; the usual classes are employer's liability or workmen's compensation, public and third-party liability, fire and special perils on assets, business interruption, and environmental impairment liability.

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Insurers require and inspect loss-prevention measures, so insurance and engineering controls reinforce each other. • Workers' safety legislation in Nepal: the Labour Act, 2074 (2017) and the Labour Rules, 2075 (2018) are the principal instruments, placing duties on the employer to provide a safe workplace, safety equipment at the employer's cost, and training, and requiring a safety and health policy and, in larger enterprises, a joint safety and health committee; they also provide for reporting of accidents and occupational disease.

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Compensation for injury and occupational disease operates through the contribution-based social security scheme under the Contribution Based Social Security Act, 2074.

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Nepal has also enacted the Disaster Risk Reduction and Management Act, 2074 (2017), which established the national disaster management structure. • Internationally, the ILO conventions on occupational safety and health and the ISO 45001 standard provide the framework most large employers follow. • Legislation is amended frequently, and thresholds, penalties and institutional arrangements change; the Acts named here are those relevant to the syllabus, but the current text must be verified against official sources before any professional reliance.

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This section covers the concepts and definitions of pollution, the sources and effects of environmental pollution of air, water and land, environmental laws and standards, and the design of pollution abatement systems for particulate matter and gaseous constituents.

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Concepts and Definitions • Pollution is the introduction into the environment of a substance or energy at a rate or concentration that causes harm to human health, living resources, ecosystems, or amenity.

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A pollutant is the agent, and a contaminant is a substance present where it does not belong, which becomes a pollutant when it causes harm. • Primary pollutants are emitted directly — sulphur dioxide, nitrogen oxides, carbon monoxide, particulates; secondary pollutants form in the atmosphere from them — ozone, peroxyacetyl nitrate, sulphuric and nitric acid aerosols, and photochemical smog.

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Ground-level ozone is the classic secondary pollutant, and is not emitted by anything — a standard examination point. • Point sources are discrete and identifiable, such as a stack or an outfall; non-point (diffuse) sources are spread out, such as agricultural runoff and urban drainage, and are much harder to regulate and control.

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Air Pollution Pollutant Principal sources Effects Particulate matter (PM10, PM2.5) Combustion, construction, road dust, industrial processes Respiratory and cardiovascular disease;

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PM2.5 penetrates deep into the lungs and is the most damaging to health; visibility loss Sulphur dioxide Combustion of sulphur-bearing fuel, smelting, sulphuric acid plants Respiratory irritation; acid rain; damage to vegetation and buildings Oxides of nitrogen High-temperature combustion, vehicles, nitric acid plants Respiratory effects; acid rain; precursor of ozone and photochemical smog Carbon monoxide Incomplete combustion, especially vehicles Chemical asphyxiant; binds haemoglobin Volatile organic compounds Solvents, coatings, refineries, fuel evaporation Ozone precursors; some are toxic or carcinogenic Ground-level ozone Secondary, from NOx and VOC in sunlight Respiratory damage; crop and material damage; the marker of photochemical smog Greenhouse gases CO₂ from combustion;

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CH₄ and N₂O from agriculture and waste Climate change Ozone-depleting substances CFCs, halons, carbon tetrachloride (historic) Stratospheric ozone depletion; controlled by the Montreal Protocol • Keep the three global issues distinct, because they are regularly confused in questions: acid rain is caused by SO₂ and NOx; stratospheric ozone depletion by CFCs and halons; and climate change by CO₂, CH₄, N₂O and fluorinated gases.

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Ozone depletion and climate change are different phenomena with different causes and different treaties. • Dispersion: emission concentration at ground level depends on the effective stack height (physical height plus plume rise), wind speed, and atmospheric stability.

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A temperature inversion traps pollutants near the ground and is the classic cause of severe smog episodes.

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The environmental lapse rate compared with the adiabatic lapse rate determines stability: a superadiabatic lapse rate gives unstable, well-mixed conditions and good dispersion, while an inversion gives extremely stable conditions and very poor dispersion.

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Plume behaviour is described as looping, coning, fanning, lofting, fumigating and trapping.

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A tall stack disperses but does not reduce emission — it exports the problem rather than solving it, which is why tall stacks are no longer regarded as an acceptable control measure on their own.

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Air Pollution Control Equipment Device Principle Effective particle size Comments Gravity settling chamber Gravitational settling in a low-velocity chamber Above about 50 μm Very simple and cheap; low efficiency; used only as a pre-cleaner Cyclone Centrifugal force in a vortex Above about 10 μm (high-efficiency units to 5 μm) No moving parts, low cost, handles high loading and temperature; efficiency rises as diameter falls, hence multiclones Fabric filter (baghouse) Filtration through a fabric, aided by the collected dust cake Down to below 1 μm Very high efficiency (over 99 %); limited by gas temperature and by moisture, which blinds the bags Electrostatic precipitator Particles are charged in a corona and collected on plates of opposite polarity Down to below 1 μm Very high efficiency with very low pressure drop; high capital cost; performance depends strongly on dust resistivity Venturi scrubber Particles are captured by atomised droplets in a high-velocity throat Down to below 1 μm Handles sticky, corrosive and hot gas and absorbs gases too; very high pressure drop and generates a liquid effluent Spray tower / wet cyclone Impaction on falling droplets Above about 10 μm Low pressure drop; also cools and absorbs • The selection logic, which is the point of the table: coarse particles are removed by settling chambers and cyclones; fine particles need a fabric filter or an electrostatic precipitator; and a wet scrubber is chosen where gaseous pollutants must be removed as well, or where the dust is sticky, hot or explosive.

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Where very high efficiency is needed on a heavy dust loading, a cyclone is used as a pre-cleaner ahead of a baghouse or precipitator. • Electrostatic precipitator resistivity is the practical limitation worth knowing: if the dust resistivity is too low the particles lose their charge and are re-entrained; if too high, back corona develops and efficiency collapses.

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Conditioning the gas with a small amount of sulphur trioxide or moisture is used to bring resistivity into the workable range. • Gaseous pollutant control: absorption in a scrubbing liquid (the commonest, as in flue gas desulphurisation with lime or limestone slurry, which produces gypsum); adsorption on activated carbon for organic vapours and odours; thermal or catalytic incineration for VOCs, catalytic units operating at much lower temperature and so at lower fuel cost; condensation for high concentrations of recoverable solvent; and biofiltration for dilute odorous streams. • Nitrogen oxides are controlled either at source by low-NOx burners, flue gas recirculation and staged combustion, or downstream by selective catalytic reduction with ammonia over a catalyst, and selective non-catalytic reduction at high temperature without one.

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SCR is more efficient but costlier;

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SNCR is simpler but needs a narrow temperature window.

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Water and Land Pollution, and Environmental Law • Water pollutants are grouped as oxygen-demanding organic wastes, nutrients (nitrogen and phosphorus), pathogens, toxic metals and organics, suspended solids, thermal discharges, oil and acids or alkalis. • The key indices, whose definitions and relation must be known:

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BOD is the oxygen consumed by micro-organisms in oxidising biodegradable organic matter, conventionally measured over five days at 20 °C;

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COD is the oxygen required to oxidise all chemically oxidisable matter, measured in a few hours with a strong oxidant; and TOC measures total organic carbon directly.

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COD is always greater than BOD, because it includes matter that micro-organisms cannot degrade, and a high BOD/COD ratio, above about 0.5, indicates a readily biodegradable effluent suitable for biological treatment, while a low ratio indicates that physico-chemical treatment is needed. • Eutrophication is the enrichment of a water body with nutrients, causing algal blooms that die and decay, consuming dissolved oxygen and killing fish.

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Phosphorus is usually the limiting nutrient in fresh water and nitrogen in coastal water, which is why phosphate was removed from detergents. • Thermal pollution reduces the solubility of oxygen while simultaneously increasing biological oxygen demand — a double effect worth stating. • Land pollution arises from uncontrolled dumping, leachate from landfills, industrial sludges, mine tailings, pesticides and fertilizer residues, and spills, and causes soil degradation, groundwater contamination and entry of contaminants into the food chain. • Environmental law in Nepal: the Environment Protection Act, 2076 (2019) and the Environment Protection Rules, 2077 (2020) are the principal instruments; they replaced the Environment Protection Act, 2053 (1996) and provide for environmental assessment, pollution control, and penalties and compensation on the polluter-pays principle.

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Assessment is tiered as Brief Environmental Study, Initial Environmental Examination and Environmental Impact Assessment, according to the scale and sensitivity of the proposal.

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Nepal has issued national ambient air quality standards and generic and industry-specific effluent standards under this framework, and Kathmandu Valley has had specific vehicle and brick-kiln measures. • Internationally: the Montreal Protocol on ozone-depleting substances, the Basel Convention on transboundary movement of hazardous waste, the Stockholm Convention on persistent organic pollutants, the Minamata Convention on mercury, and the UNFCCC with the Paris Agreement on climate change. • Standards and legislation are revised periodically; the specific limits, categories and thresholds must be checked against the current official publications before professional use.

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This section covers the management of industrial waste through reuse and recycling, the impact of pollution on the environment and its assessment, the magnitude of the industrial waste problem, hazardous waste disposal and effluents, and effluent standards and stream standards.

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The Waste Hierarchy • The waste management hierarchy, in order of preference, is the organising principle of the whole section: • 1.

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Prevention (source reduction) — do not generate the waste in the first place; always the cheapest and most effective option. • 2.

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Minimisation — reduce the quantity and hazard of what is generated. • 3.

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Reuse — use the material again for the same or another purpose without reprocessing. • 4.

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Recycling — reprocess into new material. • 5.

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Recovery — extract value, typically energy, from what cannot be recycled. • 6.

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Treatment and disposal — the last resort, with landfill at the very bottom. • The essential contrast asked for is between end-of-pipe treatment, which deals with waste after it is made and simply moves the problem from one medium to another, and source reduction, which prevents its formation — the latter being superior in both cost and effect.

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Wastewater Treatment Stage Operations Removes Preliminary Screening, grit removal, oil and grease skimming, flow equalisation Coarse solids, grit, floating matter; protects downstream units Primary Sedimentation, often with coagulation and flocculation Settleable suspended solids and some BOD (about 30 %) Secondary (biological) Activated sludge, trickling filter, rotating biological contactor, oxidation pond, UASB and other anaerobic reactors Dissolved and colloidal biodegradable organics; typically 85-95 % of remaining BOD Tertiary (advanced) Filtration, nutrient removal, adsorption on carbon, membranes, ion exchange, disinfection Residual solids, nitrogen and phosphorus, refractory organics, pathogens Sludge handling Thickening, digestion (aerobic or anaerobic), conditioning, dewatering, drying, disposal or use Reduces volume and stabilises the solids; anaerobic digestion also yields biogas • Activated sludge is the standard secondary process: wastewater is aerated with a suspension of micro-organisms, then settled in a secondary clarifier, with part of the settled sludge returned to maintain the biomass and the remainder wasted.

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Its performance is controlled by the food-to-microorganism ratio, the mixed liquor suspended solids concentration, the sludge age (mean cell residence time) and the dissolved oxygen level.

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Bulking, in which filamentous organisms prevent the sludge from settling, is its commonest operating problem. • Anaerobic treatment is preferred for high-strength effluents, because it produces methane rather than consuming energy for aeration and generates far less sludge; it is slower, more sensitive to temperature and shock, and normally needs aerobic polishing afterwards.

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The contrast between aerobic and anaerobic treatment is a standard question. • Physico-chemical treatment covers neutralisation, chemical precipitation of metals as hydroxides or sulphides, oxidation and reduction (for example reduction of hexavalent to trivalent chromium before precipitation, and cyanide destruction by alkaline chlorination), coagulation, adsorption, ion exchange, membranes and advanced oxidation processes. • A cardinal rule of industrial effluent management: segregate streams at source and treat each by the method appropriate to it, rather than mixing everything and diluting a concentrated toxic stream into a large volume that is then harder and more costly to treat.

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Dilution is never a treatment method, and discharge standards are written to prevent it being used as one.

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Hazardous Waste • A waste is hazardous if it exhibits ignitability, corrosivity, reactivity or toxicity, or if it is specifically listed.

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The four characteristics should be learnt as a set. • Management follows the cradle-to-grave principle: the generator remains responsible for the waste from its production through transport, treatment and final disposal, tracked by a manifest system. • Treatment and disposal options: physical and chemical treatment; stabilisation and solidification, which immobilise the contaminants in a cement or polymer matrix; high-temperature incineration, which is the preferred route for organic hazardous waste and which requires adequate temperature, residence time and turbulence — the three Ts of good combustion — together with rigorous flue gas cleaning; secure engineered landfill with double liners, leachate collection and long-term monitoring; and deep well injection where geology permits. • Chlorinated organic waste requires particular care, since incomplete combustion can form dioxins and furans; adequate temperature, a minimum residence time and rapid quenching through the temperature window in which they reform are the standard precautions. • The Basel Convention controls the transboundary movement of hazardous waste, principally to prevent its export from developed to developing countries.

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Standards and Impact Assessment • The two kinds of standard must be distinguished, and this is examined directly: • Effluent (emission) standards set the maximum permitted concentration or load in the discharge itself, at the point it leaves the plant.

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They are easy to monitor and enforce and apply equally to every discharger, but take no account of how much the receiving body can actually absorb. • Stream (ambient or receiving water) standards set the quality to be maintained in the receiving water body itself, according to its designated use — drinking supply, bathing, fisheries, irrigation or industrial cooling.

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They relate directly to environmental protection but require knowledge of the assimilative capacity, are harder to enforce, and can allow a discharger to exploit the dilution available. • Most regulatory systems apply effluent standards as the primary enforceable requirement, with stream standards used to decide where more stringent limits are needed. • Environmental impact assessment is the systematic process of predicting the environmental consequences of a proposal before it is authorised.

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Its steps are screening (does it need an assessment and at what level), scoping (which issues matter), baseline study, impact prediction and evaluation, identification of mitigation measures, preparation of the report, public consultation and hearing, review and decision, and finally monitoring and auditing of the actual outcome.

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Public consultation is a mandatory element, not an optional one. • In Nepal the tiers are the Brief Environmental Study, the Initial Environmental Examination and the full Environmental Impact Assessment, prescribed by the schedules to the Environment Protection Rules according to the type and size of the proposal.

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The schedules are revised from time to time, so the applicable threshold for any particular project must be checked against the current Rules.

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This section covers solid waste disposal and the recovery of useful products through process modification, recovery of by-products, energy recovery, waste utilisation, recycle and reuse, waste minimisation, environmental policy, acts and regulations, ISO 14001, and the concept of cleaner production.

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Solid Waste Management • Functional elements of a solid waste management system, in order: generation, on-site handling and storage, collection, transfer and transport, processing and recovery, and final disposal. • Segregation at source is the single most important step, because once wet organic waste is mixed with dry recyclables, both are contaminated and the value of each is largely lost.

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This is why collection systems separate organic, recyclable and residual fractions. • Composting is the aerobic biological decomposition of organic waste to a stable humus-like product.

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It requires a carbon-to-nitrogen ratio of about 25 to 30, moisture of 50-60 per cent, and aeration with turning; the process passes through a thermophilic phase reaching 55-65 °C, which destroys pathogens and weed seeds.

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Vermicomposting uses earthworms at lower temperature. • Anaerobic digestion of the organic fraction produces biogas and a digestate usable as a soil conditioner, and is preferable to composting where energy recovery is wanted and the waste is wet. • Incineration with energy recovery reduces waste volume by about 90 per cent and mass by about 70 per cent, and produces steam or electricity; it requires extensive flue gas cleaning and leaves bottom ash and a hazardous fly ash. • Sanitary landfill, as described in Chapter 5, is engineered with a liner, leachate collection and treatment, gas extraction, daily cover and post-closure monitoring, and is fundamentally different from an open dump, which has none of these.

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Landfill gas is roughly half methane, and capturing it is beneficial even if the energy is not used, because methane is a far more potent greenhouse gas than carbon dioxide. • Refuse-derived fuel is prepared by separating, shredding and drying the combustible fraction for use in cement kilns and boilers — cement kilns being particularly suitable because their high temperature and long residence time destroy organics completely and the ash is incorporated into the clinker.

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Waste Minimisation and Recovery • The four routes to waste minimisation should be known as a set, since questions ask for them by name: • 1.

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Process modification — change the route, catalyst, solvent or operating conditions so that less waste is formed; the most fundamental approach. • 2.

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Good housekeeping and operating practice — prevent leaks, spills, overfilling and unnecessary washing; often achieves substantial reduction at almost no capital cost. • 3.

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Recycle and reuse — return material to the process, either directly or after recovery. • 4.

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By-product recovery — convert a waste into a saleable product, which turns a disposal cost into a revenue. • Examples of by-product recovery worth quoting: gypsum from flue gas desulphurisation; sulphur from refinery gas by the Claus process; glycerine from soap manufacture; ammonium sulphate from coke oven gas; fly ash and blast furnace slag as cement blending materials; molasses and bagasse from sugar; and the recovery of chemicals and energy from kraft black liquor. • Energy recovery within a plant is pursued through heat integration and pinch analysis, waste heat boilers, combined heat and power, and the recovery of pressure energy in expanders. • Industrial symbiosis (industrial ecology) extends the idea beyond the plant boundary: the waste of one industry becomes the raw material of another, as in the well-known Kalundborg arrangement.

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Cleaner Production and Environmental Management Systems • Cleaner production is defined by UNEP as the continuous application of an integrated preventive environmental strategy to processes, products and services to increase efficiency and reduce risks to humans and the environment. • The definition should be unpacked for the examination: for processes it means conserving raw materials and energy, eliminating toxic materials and reducing the quantity and toxicity of emissions before they leave the process; for products it means reducing impacts over the whole life cycle from raw material to disposal; and for services it means incorporating environmental concerns into design and delivery. • The crucial characteristic is that it is preventive and applied at source, not a control measure applied afterwards — so it is the opposite of end-of-pipe treatment, which is the contrast examinations ask for.

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Cleaner production usually pays for itself, because material not wasted is material not bought. • Life cycle assessment (LCA) evaluates environmental impact from raw material extraction through manufacture, use and final disposal — cradle to grave, and its stages are goal and scope definition, inventory analysis, impact assessment and interpretation.

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Cradle-to-cradle design goes further, aiming for materials to be recovered indefinitely rather than disposed of. • ISO 14001 specifies the requirements for an environmental management system, built on the same plan-do-check-act cycle as ISO 9001 and ISO 45001.

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What is certified is the management system, not the environmental performance of the product or the plant, and commitment to legal compliance and to continual improvement are its core requirements.

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This point — that ISO 14001 certifies a system rather than a performance level — is examined directly.

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The ISO 14000 family also covers environmental auditing, labelling, life cycle assessment and greenhouse gas accounting. • Environmental policy and instruments: the polluter pays principle (the cost of pollution is borne by the one who causes it), the precautionary principle (lack of full scientific certainty is not a reason to postpone measures against serious or irreversible harm), the principle of sustainable development (meeting present needs without compromising the ability of future generations to meet theirs), and extended producer responsibility (the producer is responsible for the product at end of life).

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Instruments are regulatory (standards, permits, bans), economic (taxes, charges, tradable permits, deposit-refund schemes) and voluntary (agreements, certification, labelling). • In Nepal, the Environment Protection Act, 2076 and Rules, 2077 provide the statutory framework, supported by the Solid Waste Management Act, 2068 (2011), which assigns primary responsibility for municipal solid waste management to local bodies and provides for segregation at source and for private sector participation.

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These instruments are amended from time to time and responsibilities have shifted with federal restructuring, so the current position must be verified against official sources.

1

This section covers quality and quality control, quality circles, total quality management, quality management systems, standardization and certification, the Nepal Standard (Certification Mark) Act 2037 and Regulation 2040, and the Consumer Protection Act.

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Quality, Control and Assurance • Quality is defined as the degree to which a set of inherent characteristics fulfils requirements, or in Juran's shorter phrase, fitness for purpose.

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Quality is defined by the customer's requirements, not by the manufacturer's opinion, and the requirement may be stated, implied or obligatory. • The distinction that is examined more often than any other in this section: • Quality control (QC) is the operational technique of checking the product or process to detect defects — it is product oriented, detective, and takes place after or during production. • Quality assurance (QA) is the set of planned and systematic activities that provide confidence that requirements will be met — it is process oriented, preventive, and takes place before and throughout production. • The slogan to remember is that quality cannot be inspected into a product; it must be built in.

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Inspection sorts good from bad but adds no value and does not reduce the number of defects made. • Costs of quality are grouped as prevention costs (training, planning, process capability studies), appraisal costs (inspection and testing), internal failure costs (scrap and rework found before delivery) and external failure costs (warranty, recall, complaints and lost reputation).

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The invariable finding is that money spent on prevention reduces total cost, because external failure is by far the most expensive category.

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Statistical Quality Control • Variation is present in every process, and its two kinds must be distinguished: common cause (chance, random) variation is inherent in the process and gives a stable, predictable pattern; special cause (assignable) variation comes from an identifiable external cause such as a tool wearing, a new batch of raw material or an untrained operator.

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A process subject only to common cause variation is said to be in statistical control — which does not mean it is producing acceptable product, merely that it is predictable. • Control charts plot a statistic against time with a centre line and upper and lower control limits, conventionally set at three standard deviations from the mean.

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A point outside the limits, or a non-random pattern such as a run of seven on one side or a steady trend, signals a special cause that should be investigated. • Variables charts (for measured data) are the X-bar chart for the process mean and the R or s chart for the spread, always used as a pair.

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Attributes charts (for counted data) are the p chart for the fraction defective, the np chart for the number defective, the c chart for the number of defects per unit and the u chart for defects per unit where the sample size varies. • Control limits are calculated from the process data and describe what the process actually does; specification limits are set by the customer or the designer and describe what is wanted.

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The two are entirely different things and must never be drawn on the same chart — a standard examination trap. • Process capability compares the two:

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Cp = (USL − LSL)/6σ measures the potential capability assuming the process is centred, while Cpk accounts for actual centring and is never greater than Cp.

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A value of 1.33 is the usual minimum acceptable and 1.0 means the process output just fills the specification with no margin at all. • The seven basic quality tools should be known as a list: check sheet, histogram, Pareto chart, cause-and-effect (Ishikawa or fishbone) diagram, scatter diagram, control chart and stratification or flow chart.

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The Pareto chart applies the 80-20 rule, directing effort at the vital few causes responsible for most of the defects, and the fishbone diagram organises possible causes under headings such as man, machine, material, method, measurement and environment. • Acceptance sampling judges a lot from a sample and carries two risks: the producer's risk (α), that a good lot is rejected, and the consumer's risk (β), that a bad lot is accepted.

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The operating characteristic curve describes the plan's discriminating power; the AQL is the quality level considered acceptable and the LTPD the level the consumer wishes to reject.

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Quality Circles and Total Quality Management • A quality circle is a small voluntary group of employees from the same work area, typically six to twelve people, who meet regularly to identify, analyse and solve work-related quality and productivity problems, and to present their solutions to management.

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The defining features are that participation is voluntary, the members come from the same work area, the group chooses its own problems, and it is trained in the basic quality tools.

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The idea originated in Japan with Ishikawa. • Total Quality Management (TQM) is an organisation-wide approach in which quality is the responsibility of everyone, continuous improvement is pursued indefinitely, and decisions are based on data.

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Its principles are customer focus, total employee involvement, a process-centred approach, an integrated system, strategic and systematic planning, continual improvement, fact-based decision making and effective communication. • Key concepts: kaizen (continuous incremental improvement by everyone), the internal customer (the next process is your customer), PDCA or the Deming cycle (plan-do-check-act), benchmarking against the best, poka-yoke (mistake proofing so that an error cannot occur or cannot pass undetected), and 5S workplace organisation. • The quality gurus, whose contributions are sometimes asked for by name:

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Deming (fourteen points, the PDCA cycle, statistical thinking and the insistence that most problems are due to the system rather than the worker), Juran (the quality trilogy of planning, control and improvement, and fitness for use), Crosby (zero defects, and quality is conformance to requirements, and quality is free), Ishikawa (quality circles and the cause-and-effect diagram) and Taguchi (the loss function and robust design using design of experiments). • Six Sigma pursues a defect rate of 3.4 parts per million through the DMAIC cycle — define, measure, analyse, improve, control, using trained practitioners in a belt hierarchy; it is data driven and project based, and is often combined with lean methods as Lean Six Sigma.

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Standardization, Certification and Consumer Protection • Standardization is the establishment of agreed specifications and procedures, and its benefits are interchangeability, fitness for purpose, safety, compatibility, variety reduction, easier trade and a common technical language. • Levels: company, national (NS in Nepal, BIS in India, BS in the United Kingdom), regional and international (ISO, IEC and the Codex Alimentarius for food). • ISO 9001 specifies requirements for a quality management system, and its current principles are customer focus, leadership, engagement of people, process approach, improvement, evidence-based decision making and relationship management.

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It is built on the plan-do-check-act cycle with risk-based thinking.

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As with ISO 14001, what is certified is the system, not the product, and this distinction is examined directly.

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Certification is granted by an accredited third-party certification body following an audit, and is subject to periodic surveillance. • Certification and accreditation should not be confused: certification is the assessment of an organisation or product against a standard, while accreditation is the formal recognition that a certification or testing body is itself competent to carry out that assessment. • Standardization in Nepal: the Nepal Bureau of Standards and Metrology (NBSM), under the Ministry of Industry, Commerce and Supplies, is the national standards body.

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It operates under the Nepal Standard (Certification Mark) Act, 2037 (1980) and the Nepal Standard (Certification Mark) Regulation, 2040 (1984), which establish the NS certification mark, provide for its grant on application after inspection and testing, for its use only under licence, for inspection and surveillance of licensees, and for penalties for misuse or unauthorised use of the mark.

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The NS mark is voluntary for most products but mandatory for certain products notified in the interest of public health and safety.

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The Bureau also functions as the national metrology authority and as the WTO TBT enquiry point. • Consumer protection in Nepal is governed by the Consumer Protection Act, 2075 (2018) and the Consumer Protection Rules, 2076 (2019), which replaced the Consumer Protection Act, 2054 (1998).

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The Act sets out consumer rights — to be protected from the sale of goods and services that may be harmful to life, health and property; to be informed of the price, quantity, purity, quality and other particulars; to choose at a competitive price; to be heard; to seek redress against unfair trade practice; and to consumer education.

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It prohibits unfair and restrictive trade practices, black marketing, adulteration, misleading advertisement and the sale of substandard or expired goods, and provides for a central consumer protection council, inspection officers, compensation and penalties. • Legislation is amended from time to time, and the current text, thresholds and institutional arrangements should be verified against official sources before any professional reliance.