Drinking-Water Treatment and Safety Management

Introduction and context

Safe drinking water is not produced by a single treatment unit. It is the result of a controlled barrier system extending from the source catchment to the consumer’s tap. A treatment plant must remove particulate matter, natural organic matter, pathogens, undesirable chemicals, tastes and odours, and, where necessary, hardness or salinity. It must also prevent contamination during storage and distribution. Modern practice therefore combines process engineering with risk management, operational monitoring, asset management and public-health governance.

The treatment objectives depend on source-water quality, climate, land use, catchment protection, regulatory requirements, available skills, energy, chemicals and residuals-management capacity. Surface waters commonly require robust clarification, filtration and disinfection. Groundwaters may require oxidation, filtration, softening, removal of iron, manganese, arsenic, fluoride or nitrate, and disinfection where microbiological vulnerability exists. No process is universally optimal; selection must be based on measured hazards and validated performance.

Learning objectives

On completing this chapter, the reader should be able to:

1. Explain the purpose, mechanisms and limitations of the principal drinking-water treatment barriers.

2. Design or check preliminary coagulation, flocculation, sedimentation, filtration and disinfection calculations.

3. Select among softening, adsorption, ion exchange, membrane and advanced oxidation processes.

4. Develop a treatment-train and assess its resilience to changing raw-water quality.

5. Manage treatment residuals and identify environmental and occupational risks.

6. Apply water safety plan principles, critical-control concepts and performance verification.

7. Critically evaluate emerging technologies, digital monitoring and governance requirements.

1. Water-quality hazards and treatment objectives

A hazard is a biological, chemical, physical or radiological agent capable of causing harm. Risk combines the likelihood of occurrence with the severity of consequences. Important hazards include pathogenic bacteria, viruses, protozoa and helminths; turbidity and particles; natural organic matter; pesticides and industrial chemicals; nutrients; salinity; hardness; toxic metals; disinfection by-products; and contaminants introduced within the distribution system.

Treatment performance is often expressed through log removal or log inactivation. A 1-log reduction means a tenfold reduction, 2-log means a hundredfold reduction, and so forth. For a concentration-based removal, the log reduction value is

LRV = log10(C_in/C_out)

where C_in and C_out are influent and effluent concentrations in identical units. This expression assumes representative samples and concentrations above reliable analytical detection limits. It does not by itself prove that all organisms have been removed, because sampling, aggregation and analytical recovery introduce uncertainty.

The multi-barrier principle is central. Catchment protection reduces the hazard entering the plant; clarification and filtration remove organisms and particle-associated contaminants; disinfection inactivates organisms; and distribution-system integrity prevents recontamination. Barriers should be partially independent: relying on several units that all fail under high turbidity is weaker than combining physically different controls.

2. Process selection and treatment-train logic

A typical surface-water train is:

Intake and screening → pre-treatment → coagulation → flocculation → sedimentation or flotation → filtration → disinfection → storage and distribution.

Additional processes may include pH adjustment, activated carbon, ozonation, biological filtration, ion exchange, softening or membranes. A groundwater train may be shorter, for example oxidation followed by filtration and disinfection, but this should never be assumed without source characterization.

Process selection should consider:

• seasonal turbidity, colour, temperature and organic matter;
• pathogen occurrence and particle association;
• alkalinity, pH, hardness and ionic composition;
• toxic contaminants and their transformation products;
• peak flow, future demand and climate variability;
• chemical supply, operator competence, energy and maintenance;
• concentrate, sludge and backwash disposal;
• validation data and regulatory performance targets.

Jar testing, pilot studies and treatability testing are particularly important where raw water is variable or a process is sensitive to chemistry. Design values should include hydraulic and contaminant-loading margins, but excessive conservatism can increase cost and residuals without improving public health.

3. Coagulation and flocculation

3.1 Coagulation mechanisms

Many colloids remain suspended because of small size, Brownian motion and electrostatic repulsion. Coagulation destabilizes these particles by charge neutralization, double-layer compression, adsorption and interparticle bridging. Common coagulants include aluminium sulfate, ferric salts, polyaluminium chloride and, in selected applications, organic polymers.

Metal salts hydrolyse and form positively charged species and amorphous hydroxide precipitates. These precipitates can enmesh particles in a mechanism known as sweep flocculation. The reactions consume alkalinity and may change pH. Consequently, coagulant dose cannot be selected reliably from turbidity alone. pH, alkalinity, temperature, dissolved organic carbon, colour and particle characteristics are also relevant.

A simplified representation for alum is:

Al2(SO4)3 + 6H2O → 2Al(OH)3(s) + 6H+ + 3SO4^2−

The equation is an idealized stoichiometric representation; actual aqueous chemistry includes hydrolysis species and depends strongly on pH. It should not be used alone to calculate dose without accounting for commercial product strength, alkalinity and competing reactions.

3.2 Jar testing and control

A jar test normally applies rapid mixing for coagulant dispersion, a flocculation period, and quiescent settling. The operator compares residual turbidity, colour, dissolved organic carbon and, where relevant, particle counts across doses and pH values. The best dose is not necessarily the dose giving the lowest turbidity in one test: it should provide a stable floc, acceptable settled-water quality, manageable sludge production and adequate downstream filter performance.

Online streaming-current or zeta-potential measurements may support control, but they are surrogate indicators and require site-specific calibration. Feedback should include direct water-quality outcomes rather than relying on one instrument.

3.3 Flocculation

Flocculation is gentle mixing that promotes collisions and growth of settleable or floatable aggregates. The velocity gradient, G, represents mixing intensity, while detention time is t. A commonly used design indicator is the Camp number:

Gt = G × t

where G has units s⁻¹, t is in seconds, and Gt is dimensionless. For a basin with power input P, water volume V and dynamic viscosity μ, an idealized relation is:

G = (P/(μV))^0.5

This relation assumes that power is dissipated throughout the basin and is useful for preliminary design. Short-circuiting, compartmentalization, floc breakage and non-uniform turbulence mean that actual performance must be verified hydraulically and operationally. Multi-stage flocculation commonly uses decreasing intensity to grow flocs without destroying them.

4. Sedimentation and dissolved-air flotation

4.1 Sedimentation principles

In ideal discrete-particle settling, removal is related to overflow rate rather than simply detention time. The surface overflow rate is

v_o = Q/A_s

where Q is flow and A_s is plan surface area. Under ideal assumptions, a discrete particle with settling velocity v_s is theoretically captured when v_s ≥ v_o. This is a conceptual design relationship, not a guarantee of field performance. In practice, inlet and outlet hydraulics, density currents, wind, flocculation, sludge accumulation and particle-size distributions affect removal.

For a basin of volume V, nominal detention time is

t_d = V/Q.

Detention time describes hydraulic capacity but is not a direct measure of particle removal. A basin can have adequate nominal detention time and poor performance because of short-circuiting or resuspension.

For flocculent settling, particles change size and settling velocity as they descend. Column settling tests and solids-flux analysis are more appropriate than applying a single discrete-particle velocity. Sludge must be withdrawn regularly to prevent anaerobic conditions, gas formation and solids carryover.

4.2 Dissolved-air flotation

Dissolved-air flotation (DAF) attaches fine air bubbles to flocs, causing them to rise. It is particularly useful for low-density algae, colour-associated material and waters that produce poorly settling floc. DAF requires air saturation, recycle control, effective flocculation and reliable surface-skimmer operation. It may use less basin area than sedimentation but is more sensitive to hydraulic and mechanical control.

5. Filtration

5.1 Granular-media filtration

Rapid gravity filters typically contain stratified media such as anthracite, sand and support gravel. Water passes through the bed while particles are removed by straining, interception, sedimentation within pores, attachment and, in some systems, biological activity. Removal is not simply a sieve effect. Filter ripening, media condition, coagulant chemistry and influent particle properties are important.

The hydraulic loading or filtration rate is

v_f = Q/A_f

where Q is the filter flow and A_f is the effective filter area. This equation is dimensionally valid when consistent units are used. The selected rate must conform to media characteristics, pretreatment quality and validated performance; a higher rate may reduce capital cost but increase head loss and breakthrough risk.

Head loss increases as the bed accumulates solids. Filters are backwashed when terminal head loss, effluent turbidity, particle counts or filter run time reaches an operational limit. Backwash flow must expand and clean the bed without excessive media loss. Backwash water and filter-to-waste periods should be managed so that disturbed solids are not sent directly to consumers.

5.2 Slow sand and biologically active filtration

Slow sand filters operate at low filtration rates and rely substantially on a biologically active surface layer, the schmutzdecke. They can provide excellent pathogen and particulate reduction but require large land areas and careful control of pretreatment and cleaning. Biologically active rapid filters can remove biodegradable organic matter and some taste-and-odour compounds, but performance depends on temperature, oxygen, empty-bed contact time and microbial acclimation.

5.3 Membrane filtration

Microfiltration and ultrafiltration physically remove particles and many microorganisms; nanofiltration and reverse osmosis additionally remove dissolved organic and inorganic constituents. Membrane flux is commonly expressed as

J = Q_p/A_m

where J is permeate flux, Q_p is permeate flow and A_m is membrane area. Transmembrane pressure, temperature, concentration polarization and fouling influence flux. Membrane systems require integrity monitoring, cleaning strategies and management of concentrate. A membrane with a nominal pore-size designation is not automatically a validated pathogen barrier; integrity testing and organism-specific performance evidence are required.

6. Disinfection and by-product control

Disinfection aims to inactivate pathogens after physical removal has reduced turbidity and particle shielding. Chlorine, chloramine, ozone, ultraviolet (UV) radiation and, in some settings, chlorine dioxide are used. Disinfection is distinct from sterilization: practical water treatment seeks an appropriate public-health level of inactivation, not absolute elimination of every organism.

For many chemical disinfectants, a useful conceptual relationship is the CT value:

CT = C × T

where C is disinfectant concentration, usually in mg/L, and T is effective contact time, in minutes; CT therefore has units mg·min/L. Required CT depends on organism, pH, temperature, disinfectant form and target log inactivation. The effective contact time is not necessarily the theoretical basin detention time. It should account for baffling and short-circuiting, often through a validated baffling factor or tracer study.

For a first-order inactivation model, when its assumptions are appropriate:

N/N0 = e^(−kCt)

where N0 and N are viable organism concentrations before and after exposure, k is an empirical coefficient, C is disinfectant concentration and t is exposure time. Real systems often depart from this simple model because disinfectant decays, organisms aggregate, water chemistry changes and populations have varied resistance. Regulatory tables and validated studies should therefore govern final design.

Chlorination provides a residual throughout distribution, but reacts with natural organic matter to form disinfection by-products such as trihalomethanes and haloacetic acids. Control measures include improved coagulation, precursor removal, optimized dosing, breakpoint control, alternative disinfectants, biologically active filtration and management of water age. Chloramine can provide a longer-lasting residual but may generate different by-products and can cause nitrification if poorly controlled. UV is effective against many organisms without adding a persistent residual; it therefore normally requires a separate residual strategy where distribution protection is needed. Ozone is a strong oxidant but may form bromate in bromide-containing waters and generally requires downstream biological stabilization.

7. Softening and targeted chemical treatment

7.1 Lime-soda softening

Hardness is principally caused by calcium and magnesium. Lime softening raises pH and precipitates calcium carbonate and magnesium hydroxide. Soda ash may be added when non-carbonate calcium hardness requires additional carbonate. The process produces substantial sludge and requires pH control, recarbonation and solids management. Softening should be justified by scaling, soap consumption, aesthetic or process requirements; hardness is not ordinarily a pathogen hazard.

7.2 Ion exchange

Cation exchange resins replace calcium and magnesium with sodium or, in specialized systems, hydrogen ions. Anion exchange can remove nitrate, arsenate or other anions, but selectivity, competing ions, regeneration chemicals and brine disposal must be considered. Exhaustion monitoring and breakthrough control are essential because a resin can appear hydraulically normal while contaminant leakage increases.

7.3 Adsorption and oxidation

Granular activated carbon removes many organic compounds through adsorption and can support biodegradation. Its effectiveness depends on contaminant properties, carbon type, contact time, empty-bed life and competing natural organic matter. Powdered activated carbon is dosed and removed with solids but requires reliable feed and residual handling.

Oxidation processes using ozone, hydrogen peroxide, UV or combinations can transform micropollutants. Transformation does not always mean detoxification: by-products must be identified where relevant, and biodegradability may increase. Advanced oxidation should therefore be assessed by contaminant mass balance, toxicity, energy use and post-treatment requirements, not solely by disappearance of the parent compound.

8. Membrane and advanced treatment selection

Reverse osmosis and nanofiltration are powerful barriers for salts, many metals, nitrate, PFAS and other dissolved constituents, depending on membrane chemistry and operating conditions. Their disadvantages include high energy demand, concentrate disposal, pretreatment requirements and mineral removal that may require stabilization or remineralization. Membrane treatment is most defensible when the target contaminant cannot be reliably removed by lower-energy processes or when multiple dissolved hazards occur together.

A decision matrix should compare health benefit, reliability, life-cycle cost, energy, chemical use, residuals, greenhouse-gas implications, operator requirements and failure consequences. Pilot testing should examine realistic seasonal water, not only ideal laboratory water. Treatment trains should also be designed for upset conditions, including coagulant failure, membrane integrity loss, power interruption and unusual algal or chemical events.

9. Residuals management

Water treatment residuals include screening waste, coagulation sludge, softening solids, spent activated carbon, membrane concentrate and filter backwash. They may contain concentrated metals, pathogens, coagulant chemicals, natural organic matter or regulated contaminants. Disposal to a watercourse is not acceptable merely because the original water was potable-source water; concentration and chemical transformation can change environmental risk.

A residuals plan should characterize quantity and composition, segregate incompatible streams, minimize water content, recover useful materials where feasible, and select disposal or beneficial use under applicable environmental law. Sludge thickening, dewatering and drying reduce transport volume. Recycling filter backwash can conserve water but may recycle pathogens or contaminants; it should be settled, disinfected or otherwise controlled and returned at a managed rate. Concentrate from membranes requires site-specific assessment of aquatic toxicity, receiving-water capacity and alternatives such as sewer discharge, deep-well injection or further concentration.

Workers require protection from chlorine, ozone, coagulant dust, confined spaces, biological aerosols, high-pressure equipment and electrical hazards. Chemical storage must include segregation, secondary containment, emergency showers, gas detection and compatible materials.

10. Water safety plans and operational risk management

A water safety plan (WSP) is a preventive, system-wide method for ensuring safe drinking water. It typically includes:

1. system description, including catchment, treatment, storage and distribution;

2. hazard identification and risk assessment at each step;

3. control measures and critical operational limits;

4. monitoring and corrective actions;

5. verification, validation and independent review;

6. documentation, communication and continual improvement.

A critical control point is a step where control is essential and a measurable operational limit can be applied. Examples include minimum disinfectant residual, validated UV dose, filter effluent turbidity, membrane integrity, coagulant pH range or secure reservoir status. Not every important activity is a critical control point; maintenance, catchment enforcement and laboratory quality assurance may be prerequisite programmes or supporting controls.

Validation asks whether a control is capable of achieving the required outcome under defined conditions. Verification asks whether the system is operating as intended. Operational monitoring is frequent and supports immediate action; compliance monitoring demonstrates conformity with standards; surveillance may be undertaken by public-health authorities.

Risk assessment should address normal operation, start-up, shutdown, floods, droughts, fires, cyber incidents, chemical spills, equipment failure and deliberate contamination. Emergency plans should specify authority, communication pathways, alternative supplies, public notification criteria and post-event investigation. A WSP is ineffective if it exists only as a document; operators must have training, authority to act and resources to maintain barriers.

11. Applied case: illustrative treatment-train assessment

Background

A fictional municipality draws water from a eutrophic reservoir. During summer, turbidity varies from 3 to 35 NTU, algal activity increases, and dissolved organic carbon reaches 7 mg/L. The existing plant uses alum coagulation, flocculation, sedimentation, rapid sand filtration and chlorination. Complaints concern taste and odour, while treated-water trihalomethanes approach the regulatory limit.

Problem analysis

Jar tests show that the existing alum dose is adequate at moderate turbidity but leaves elevated dissolved organic carbon during algal episodes. Algal cells occasionally pass clarification and cause rapid filter head-loss development. The contact tank has a nominal detention time of 30 minutes, but tracer testing indicates an effective contact time of 18 minutes at peak flow. Chlorine demand and water age together increase by-product formation.

The risk is not solved by simply increasing chlorine. Higher chlorine can worsen by-products, while excessive coagulant can increase sludge and aluminium residuals. The system requires improved precursor removal, algae control and better hydraulic management.

Approach and solution

The municipality undertakes seasonal jar testing and adjusts coagulation pH and dose using settled-water organic carbon and turbidity as outcome measures. A powdered activated-carbon trial is conducted during algal episodes. Filter-to-waste is extended after backwashing, and online particle counting is added. The contact tank is baffled to improve hydraulic efficiency, and chlorine application is moved to a point that preserves disinfection while reducing precursor reaction time. A biological activated-carbon pilot is evaluated for taste-and-odour compounds and biodegradable organic matter.

The WSP identifies reservoir algal alerts, settled-water turbidity, filter effluent particle counts, chlorine residual, effective contact time and trihalomethanes as linked control and verification indicators. An escalation procedure is established for severe blooms, including increased sampling and alternative raw-water withdrawal depth where feasible.

Outcome and learning points

The illustrative outcome is reduced taste-and-odour frequency and lower by-product formation without relying on excessive chlorine. The key lesson is that treatment optimization must consider the whole barrier sequence. Better clarification, hydraulic validation and precursor control can be more effective than increasing disinfectant dose. The case also demonstrates that seasonal pilot testing and risk-based monitoring are more defensible than fixed settings based on historical average water quality.

12. Contemporary developments and the role of digital tools

Online turbidity, UV transmittance, particle counts, conductivity, fluorescence and disinfectant sensors can improve rapid detection of process deterioration. Digital twins and machine-learning models may forecast coagulant demand, membrane fouling or disinfectant decay. However, sensor drift, missing data, model bias and changing catchment conditions can produce unsafe recommendations. AI should support, not replace, validated process knowledge, laboratory confirmation and accountable operator decisions. Cybersecurity, access control, audit trails and fail-safe manual operation are essential.

Current priorities include climate-resilient source protection, energy-efficient membranes, low-carbon chemical manufacture, PFAS and other persistent-contaminant control, improved pathogen monitoring, real-time microbial indicators, resource recovery from residuals and decentralized treatment for vulnerable communities. Emerging technologies should be judged by demonstrated health protection, life-cycle impacts and maintainability—not by novelty alone.

13. Professional best practices and limitations

Effective practice begins with representative monitoring and a clear statement of treatment objectives. Engineers should validate critical barriers, maintain calibration and laboratory quality systems, design for peak and abnormal conditions, and document assumptions. They should avoid treating regulatory compliance as proof that all risk has been eliminated. Standards differ among jurisdictions and may change; the responsible engineer must consult current national drinking-water regulations, public-health guidance, occupational-safety rules and environmental-discharge permits.

Important limitations include uncertainty in raw-water sampling, differences between pilot and full-scale hydraulics, analytical detection limits, pathogen aggregation, chemical interactions and changing climate. Cost optimization must not undermine resilience or disproportionately expose low-income communities to risk. Decisions should be transparent, evidence-based and attentive to intergenerational environmental impacts.

Chapter Summary

Drinking-water safety is achieved through multiple, independently managed barriers rather than a single treatment unit. Coagulation and flocculation destabilize and aggregate particles; sedimentation or flotation separates floc; filtration removes residual particles and organisms; and disinfection inactivates pathogens. Softening, adsorption, ion exchange, oxidation and membranes address particular chemical or aesthetic objectives but introduce energy, chemical and residuals-management considerations.

Key design relationships include log reduction, surface overflow rate, nominal detention time, filtration rate, Camp number, membrane flux and disinfectant CT. These relationships are preliminary tools whose assumptions must be checked through pilot testing, tracer studies, integrity testing and operational validation. Residuals require controlled handling, and worker safety is integral to plant design.

Water safety plans connect catchment, treatment and distribution risks through hazard assessment, control measures, operational limits, corrective action, verification and continual improvement. Digital and advanced technologies can strengthen monitoring but cannot replace validation, professional judgment, governance or accountable operators. Resilient treatment therefore combines sound engineering, public-health objectives, environmental stewardship and transparent risk management.

Key Terms

Hazard: A biological, chemical, physical or radiological agent capable of causing harm.

Risk: The likelihood and consequence of harm arising from a hazard.

Coagulation: Chemical destabilization of colloidal and fine particles.

Flocculation: Gentle mixing that promotes formation and growth of flocs.

Sweep flocculation: Particle enmeshment in precipitated hydroxide solids.

Surface overflow rate: Flow divided by the plan surface area of a settling basin.

Detention time: Basin volume divided by flow under nominal hydraulic conditions.

Filtration rate: Flow divided by effective filter area.

Filter ripening: The initial period after backwashing during which filter performance develops.

Disinfection: Inactivation of pathogenic organisms by chemical or physical means.

CT value: Product of disinfectant concentration and effective contact time.

Log removal value: Base-ten logarithm of influent concentration divided by effluent concentration.

Softening: Treatment that reduces calcium and magnesium hardness.

Ion exchange: Reversible exchange of ions between water and a solid resin.

Adsorption: Accumulation of a dissolved substance on a solid surface.

Membrane flux: Permeate flow per unit membrane area.

Concentrate: Membrane reject stream containing elevated dissolved constituents.

Water safety plan: Preventive, system-wide framework for managing drinking-water risks.

Validation: Demonstration that a control can achieve its intended performance.

Verification: Confirmation that a control system operates as intended.

Review Questions

Short Answer Questions

1. Why is a multi-barrier approach more reliable than dependence on disinfection alone?

2. Define the Camp number and state its units.

3. Distinguish nominal detention time from effective contact time.

4. Give two reasons why membrane concentrate requires specific management.

5. Differentiate validation from verification in a water safety plan.

Long Answer Questions

1. Explain the mechanisms of coagulation and flocculation and discuss how pH, alkalinity, temperature and organic matter influence coagulant selection.

2. Describe granular-media filtration, including particle-removal mechanisms, head-loss development, backwashing and operational monitoring.

3. Compare chlorine, chloramine, ozone and UV with respect to pathogen control, residual protection and disinfection by-products.

4. Discuss the selection of softening, adsorption, ion exchange, advanced oxidation and membrane processes for dissolved contaminants.

5. Explain how a water safety plan links catchment protection, treatment barriers, distribution integrity, monitoring and emergency response.

Analytical / Application Questions

1. A filter treats 18,000 m³/d through three identical filters, each 6 m wide and 12 m long. Calculate the average filtration rate in m/d, assuming equal flow distribution. Interpret one limitation of this calculation.

2. A contact tank receives 24,000 m³/d and has a volume of 750 m³. A tracer test gives a baffling factor of 0.60. Calculate the effective contact time in minutes and explain why it should be used instead of nominal detention time for CT assessment.

3. A reservoir develops recurrent algal blooms, while treated-water trihalomethanes approach the regulatory limit. Propose an integrated investigation and treatment-optimization programme, including monitoring, process changes, residuals implications and WSP controls.

Multiple Choice Questions with Answers

Question 1

What is the principal purpose of coagulation in conventional surface-water treatment?

A. To increase disinfectant residual throughout the distribution system

B. To destabilize colloidal particles so they can form removable floc

C. To remove dissolved salts by pressure-driven separation

D. To biologically nitrify ammonia

Correct Answer: B. To destabilize colloidal particles so they can form removable floc

Question 2

A sedimentation basin treats 12,000 m³/d and has a plan area of 600 m². What is its surface overflow rate?

A. 2 m/d

B. 20 m/d

C. 200 m/d

D. 7,200 m/d

Correct Answer: B. 20 m/d

Question 3

Which statement about nominal detention time is correct?

A. It always equals the actual contact time of every water parcel

B. It is calculated as basin volume divided by flow

C. It is independent of basin volume

D. It directly measures pathogen inactivation

Correct Answer: B. It is calculated as basin volume divided by flow

Question 4

A process reduces a contaminant from 100 mg/L to 0.1 mg/L. What is the log removal value?

A. 1

B. 2

C. 3

D. 4

Correct Answer: C. 3

Question 5

Which treatment is generally most directly suited to removing calcium and magnesium hardness?

A. Lime-soda softening

B. Ultraviolet irradiation

C. Screening

D. Air stripping

Correct Answer: A. Lime-soda softening

Question 6

In the expression CT = C × T, what does T represent?

A. Total plant volume

B. Effective disinfectant contact time

C. Water temperature only

D. Turbidity concentration

Correct Answer: B. Effective disinfectant contact time

Question 7

Which is a major limitation of ultraviolet disinfection?

A. It necessarily produces high trihalomethane concentrations

B. It cannot inactivate any viruses

C. It provides no persistent distribution-system residual

D. It always increases water hardness

Correct Answer: C. It provides no persistent distribution-system residual

Question 8

A membrane produces 900 m³/d of permeate using 300 m² of membrane area. What is the flux?

A. 0.3 m/d

B. 3 m/d

C. 30 m/d

D. 270,000 m/d

Correct Answer: B. 3 m/d

Question 9

Which activity is most characteristic of validation?

A. Checking whether an operator completed a log sheet

B. Demonstrating that a UV system can achieve its required pathogen reduction

C. Replacing a failed pump after an incident

D. Issuing a monthly water bill

Correct Answer: B. Demonstrating that a UV system can achieve its required pathogen reduction

Question 10

Which statement best describes a water safety plan?

A. A document limited to laboratory compliance results

B. A preventive framework covering hazards from catchment to consumer

C. A design method used only for membrane plants

D. A schedule for chemical purchasing only

Correct Answer: B. A preventive framework covering hazards from catchment to consumer