Chapter 6 Overview - Food and Agriculture Organization · Chapter 6: Overview • 91 Chapter 6...

Chapter 6: Overview • 91

Chapter 6

Overview

Weaknesses

• Aquifers are a finite resource;abstraction must be matched byrecharge rates.

• Point over-abstraction can causelocal springs and streams to dry up.

• Drying up of rivers is possible withlarge-scale over-abstraction.

• Water availability can be critical inthe development of agriculture andagro-industries.

• Shallow aquifers are open topollution with pesticides and otheragro-chemicals.

• Agro-chemicals can contaminategroundwaters to levels that breachquality standards.

• Shallow aquifers are vulnerable tocontamination with excess surfaceuse of fertilisers and other agro-chemicals.

• Aquifers are difficult to clean oncecontaminated.

• Natural chemistry of groundwatercan cause adverse health effects.

• Shallow aquifers can becontaminated with pathogens.

• Poor disposal of livestock wastecontaminates shallow aquifers withpathogens.

• Chemical components ofgroundwater can accumulate in use;for example salinity from irrigationapplications.

Strengths

• Groundwater free from microbialcontamination.

• Generally free from hazardouschemical pollution.

• Good physical quality.• Usually not affected by seasonality

of rainfall.• Disinfection desirable, but

reasonable level of protectionagainst water borne disease if goodcommunity hygiene.

• Simple hand pump abstraction ispossible.

• Pump stand protection isreasonably simple.

• Can provide water for irrigation andlivestock watering.

• Wind powered pumps are anappropriate technology.

• Aquifer area can remove the needfor lengthy water main networks.

• Deep boreholes are technicallyfeasible.

• Aquifer recharge is possible.• Generally superior quality to surface

water; cheaper to exploit.• Effectively water is stored

underground; does not take upvaluable land area.

6.1 Groundwater sources

Agro-industries, water resources and public health • 92

Weaknesses

• Places an increasing demand onvaluable and limited water suppliesin some developing countries.

• Water availability can limit thepotential for locating agro-industries, and lead to tensions.

Water collection in poor rural areasfor agricultural purposes can makeunreasonable demands on childrenand women.

Strengths

• Agro-industries can be beneficial in socio-economic terms, and can support water treatment and supply, sewerage andwastewater treatment infrastructuredevelopment.

• Can comprise more than 50 percentof the manufacturing sector indeveloping countries.

Increasing trends to reduce amountsof pesticides and fertilisers used.

6.2 Agriculture and agro - industries

Weaknesses

• Water resource monitoring andmanagement is necessary.

• Aquifers are not uniformlydistributed within regions.

• Protection zones are required insensitive aquifer catchments toprotect water quality.

• “Best practice” agricultural methodsare required in areas wheregroundwater forms a major watersource.

• Latrines must be positioned at asafe distance from the groundwaterabstraction point.

• Wells need on-going monitoringand maintenance to ensure safesupplies.

• Excessive groundwater abstractioncan lead to saline intrusion inaquifers.

6.1 Groundwater sources (cont.)


Weaknesses

• Water quality varies, typicallydepending on whether the water isfrom an upland or lowland source.

• Usually poorer physical, chemicaland microbiological quality thangroundwater.

• Large-scale agriculture can affectrainfall and run-off patterns.

• Agricultural activities can dischargepathogens into the environment.

• Pollution with agro-chemicals canexpose populations to healththreatening chemical pollution.

• Diffuse sources of agro-chemicalpollution are difficult to trace andregulate; for example fertiliserwashed off land into rivers.

• Agro-chemicals in water run-off cantrigger biological problems inponds, lakes, streams and rivers.

• Physical contamination induced byagricultural activities can affect theacceptability of potable water.

• Physical, chemical and biologicalcontamination of surface water byagricultural activities can causewater treatment problems.

• Expensive and complex watertreatment processes are required toremove agro-chemical pollution andbiological consequences.

• Legislation and enforcement areoften needed to protect waterquality.

Strengths

• Surface water is widely distributedglobally, including in rockycatchments.

• Less difficult to deal with pollutedsurface waters than groundwaters.

• Surface water intakes at treatmentworks can usually be quicklyclosed if a major pollution incidentoccurs.

• Effluent discharge quality standardscan be formulated taking intoaccount the character of thereceiving surface water.

• Monitoring and regulating regimescan be introduced to help protectwater quality.

• Improved water availability canstimulate the development ofagriculture and agro-industries.

6.3 Surface water sources


Weaknesses

• Stringent measures are necessary toavoid microbial contamination ofagricultural products and infectionof agricultural workers.

• Wastewater effluents can have anadverse effect on surface waterquality.

• Wastewater treatment often requiresthe application of high leveltechnical expertise within acomplicated system of unitprocesses.

• Human contact with surfacewaters badly contaminated withwastewater effluents can lead toinfection with water borne diseaseand exposure to chemical hazards.

• Many strong agricultural wastesplace a high demand on wastewatertreatment processes and receivingwaters.

• Unseen waste streams, such aspesticides used to remove weedsfrom agricultural rail or road freightyards, can have an adverse effect onreceiving waters (via run-off).

• Farm animals are often a reservoirfor a range of human pathogens.

• Numerous pathogens are capable ofpassing through water treatmentprocesses into supply, unlesscareful control measures are put inplace.

• Strong agricultural and agro-industry wastes are capable ofcausing severe dissolved oxygenreduction in surface waters, even upto the point of causing anaerobicconditions.

• Waste treatment processes can beadversely affected by pH.

• Screenings can be contaminatedwith pathogens and often requiresafe disposal.

• In small amounts, screenings can becomposted.

Strengths

• Wastewater can be used foragricultural purposes with sufficienttreatment.

• Rivers provide cheap, effectivedisposal routes for wastewatereffluents.

• Micro-organisms are capable ofoxidising most dissolvedagricultural wastes in suitabletreatment systems.

• Screens are suitable for thepreliminary treatment of waste.

• Sedimentation can form a reliableprimary treatment process.

• Fixed film, dispersed growth orwaste stabilisation pond systemscan be used to treat agriculturalwastes.

• Waste stabilisation ponds havelittle, if any, energy demand andcan tolerate shock loads.

• Percolating filters are able toachieve 80-90 percent BODreduction, and are able to tolerateshock loads.

• De-nitrification (nitrate reduction)of waste effluent is possible indispersed growth systems.

• Rotating biological contactors aresuitable for some small communityapplications, and have lowtechnical support requirements.

• Waste stabilisation ponds areoften effective in low technologyapplications typically comprisinganaerobic, facultative andmaturation ponds in series.

• Anaerobic ponds are effective atremoving BOD (say 75 percent)particularly at higher temperatures.

• Facultative ponds are able toremove residual waste BOD, butcan be productive.

6.4 Wastewater treatment


Weaknesses

• Percolating filters require arelatively large land area.

• Rotating biological contactors haverelatively high capital cost.

• Rotating biological contactors aregenerally not effective atwithstanding shock loads.

• Reclamation of water offers thepotential for water conservationand, when used for irrigation, theproduction of a saleable crop.

• Diffuse sources of agro-chemicalpollution are difficult to trace andregulate; for example fertiliserwashed off land into rivers.

• Agro-chemicals in water run-off cantrigger biological problems inponds, lakes, streams and rivers.

• Physical contamination induced byagricultural activities can affect theacceptability of potable water.

• Physical, chemical and biologicalcontamination of surface water byagricultural activities can causewater treatment problems.

• Expensive and complex watertreatment processes are required toremove agro-chemical pollution andbiological consequences.

• Legislation and enforcement areoften needed to protect waterquality.

Strengths

• Maturation ponds can provideeffective pathogen removal (up to99.9999 percent bacteria removal)and can be used to produce fish,although sufficient safeguards toprotect against infection fromresidual pathogens are needed.

• Tertiary treatment via maturationponds, grass plots and coarse filtersis able to protect receiving waterquality.

• Simple cascade and otherturbulence producing stages can beused to improve dissolved oxygenlevels of effluents at the point ofdischarge.

• Wastewater sludges - typicallymade up of suspended solids andbiomass removed by sedimentation- are often “strong” and arecommonly treated anaerobicallyunless a high-energy input isacceptable.

• Sludge treatment processes includedigestion, heat treatment,composting, chemical conditioning,dewatering and incineration.

• In colder climates anaerobicdigesters are generally heated tomaintain suitably short sludgestabilisation times.

• Wastewater re-use (reclamation ofwater) is becoming more common,particularly for crop irrigation.

• WHO suggests that wastewater re-use for a crop eaten raw shouldhave a low level of microbialcontamination (100/100 ml faecalcoliform).

6.4 Wastewater treatment (cont.)


Weaknesses

• Water-related diseases affect bothdeveloping and industrialisedcountries.

• Pathogens represent the mostcommon risk in drinking water, andtheir removal is the prime concernof treatment.

• Globally, approximately 80 percentof all disease and 50 percent ofhospital bed occupation are due towater related infection.

• Long term exposure to agro-chemicals at relatively low dosescan produce chronic health effects.

• Pesticides are persistent in theenvironment and the tissues ofanimals (including people).

• Organo-phosphate compounds areimplicated in chronic health effects.

• Limits are difficult to achieve inareas where natural water colour ishigh, although there is no directhealth effect.

• Most advanced water treatmentsystems are inherently unreliable,unless supported by considerabletechnical and scientific resources.

• Water treatment costs riseappreciably with the level of rawwater pollution.

• Rising demand in numerouscountries is outstripping supplycapacity, and is leading to the use ofpoorer raw water sources.

• Water supply shortfalls could lead tomilitary or political conflicts overaccess to water.

• Eutrophication can occur in storagereservoirs as a result of agro-chemical contamination of run-off.

• Severe eutrophication problems candeplete dissolved oxygen to levelswhere fish kills occur.

• Rapid gravity filters require carefullycontrolled chemical pretreatment.

Strengths

• Water treatment breaks thetransmission route of most water-related diseases.

• Best practice agricultural and publichealth engineering methodscontribute to alleviating water-related diseases.

• Guideline values for chemicalcontaminants are provided by theWorld Health Organisation (WHO).

• The logic behind guideline values isto identify unsafe contamination,but also to maintain a wholesomesupply that will continue to be usedby the community.

• The multiple barrier concept ofpathogen removal is particularlyappropriate for small communities.

• The ranges of treatmenttechnologies available permit theselection of an appropriatetechnology.

• Participation of the localcommunity is essential to supportthe development of reliablesystems.

• Protection of groundwater andsurface water catchments indeveloping countries can protectwater supplies.

• Reservoirs can offer physical,chemical and microbiological waterquality improvement as well asprotecting against seasonalshortfalls in raw water.

• Multiple takeoff points allow themixing of stored water inreservoirs.

• Coagulant addition can promotethe removal of suspended andcolloidal solids in physico-chemicalwater treatment.

• Jar tests can be carried out toestablish optimum coagulantdosing rates on a day to day basis.

6.5 Water treatment and public health


Weaknesses


• Rapid gravity filters, with upstreamchemical coagulation andclarification, do not offer reliablemicrobiological treatment.

• Slow sand filters are sensitive toinfluent raw water turbidity ofgreater than 12 NTU.

• The capital construction costs ofslow sand filters are relatively high.

• High levels of microbiologicalcontamination and excessiveloading of organic material may alsoinhibit treatment efficiency.

• Granular activated carbon filters arean expensive water treatmentprocess.

• High turbidity, high ammonia andits compounds, high pH and lowtemperatures adversely affectchlorine disinfection.

• Viruses are more resistant tochlorination than faecal coliform, asare the much larger protozoan cysts.

• It is particularly difficult for poorrural communities in developingcountries to fund the constructionand maintenance of reliable watertreatment systems.

• Simple pot chlorinators, welldisinfection and similar simpleinterventions are appropriate inpoor rural communities indeveloping countries.

• Water distribution is a majorproblem in most developingcountries with frequent pumpbreakdowns, and as much as 60percent of treated supplies are lostin leakage.

• Decreased mains pressures canallow infiltration to contaminatesupplies.

Strengths

• Coagulant aids can be added toimprove floc development inphysico-chemical treatment.

• Rapid gravity filtration is able tofilter chemically treated water.

• Air-washwater backwash processesfor rapid gravity filters facilitatecleaning.

• High technology treatment systemscan deal with most of the raw waterqualities expected.

• Dissolved air flotation can deal withwater with a high algal content.

• Dual media rapid gravity filters canoffer improved performance.

• Slow sand filters can achieve highlevels of microbiological treatmentwith 99.99 percent removal ofviruses, bacteria and otherpathogens.

• Slow sand filters can effectivelyremove protozoan cysts that areoften capable of passing throughdisinfection.

• Gravel prefilters can offer aneffective low technology means ofreducing supernatant turbidity, aswell as achieving levels of physicaland microbiological removal.

• A multistage gravel prefilter andslow sand filter system provides alow technology water treatmentsystem that complies with themultiple barrier concept.

• The running costs of gravelprefilters and slow sand filters arelow.

• WHO water quality standards areavailable.

6.5 Water treatment and public health (cont.)


Weaknesses


• Rapid gravity filters, with upstreamchemical coagulation andclarification, do not offer reliablemicrobiological treatment.

• Slow sand filters are sensitive toinfluent raw water turbidity ofgreater than 12 NTU.

• The capital construction costs ofslow sand filters are relatively high.

• High levels of microbiologicalcontamination and excessiveloading of organic material may alsoinhibit treatment efficiency.

• Granular activated carbon filters arean expensive water treatmentprocess.

• High turbidity, high ammonia andits compounds, high pH and lowtemperatures adversely affectchlorine disinfection.

• Viruses are more resistant tochlorination than faecal coliform, asare the much larger protozoan cysts.

• It is particularly difficult for poorrural communities in developingcountries to fund the constructionand maintenance of reliable watertreatment systems.

• Simple pot chlorinators, welldisinfection and similar simpleinterventions are appropriate inpoor rural communities indeveloping countries.

• Water distribution is a majorproblem in most developingcountries with frequent pumpbreakdowns, and as much as 60percent of treated supplies are lostin leakage.

• Decreased mains pressures canallow infiltration to contaminatesupplies.

Strengths

• In developing countries it is farbetter to control the spread and useof agro-chemicals than to deal withthe consequences of surface waterand groundwater pollution.

• Terminal disinfection in watertreatment systems is an effectivemeans of protecting public health.

• Chlorine is an effective disinfectant;the risks associated with by-products are minimal comparedwith those associated with waterrelated disease.

• Epidemiological evidence canpinpoint water quality problems.

• Improving the quality of watersupplies and preventing the casualuse of unprotected sources canalleviate the level of waterbornediseases in a community.

• The level of water-washed diseasesoccurring in a community can bereduced by increasing the amountof water available, improving theaccessibility and reliability ofsupply and improving hygiene.

• Water-based diseases can becombated by reducing the need forcontact with infected water,reducing levels of contaminationand controlling the aquatic vector.

• Water-related insect vectors can becontrolled by destroying breedingsites, reducing the need to visit sitesand implementing protectivemeasures.

• Holistic approaches to water-related disease problems arerequired.

• Hazard analysis can assist watersupply improvement programmesby identifying existing systemdeficiencies.rates on a day to daybasis.



Weaknesses

• Improved availability of suppliescan stimilate increased quantityusage.

• Water quality standards need to bedeveloped for developing countries.

• All water quality standards shouldbe monitored.

• The potential impact of existing andproposed agricultural activities onriver catchments is an importantmatter for consideration whenplanning the development of anarea.

Strengths

• In developing countries it is farbetter to control the spread and useof agro-chemicals than to deal withthe consequences of surface waterand groundwater pollution.

• Terminal disinfection in watertreatment systems is an effectivemeans of protecting public health.

• Chlorine is an effective disinfectant;the risks associated with by-products are minimal comparedwith those associated with waterrelated disease.

• Epidemiological evidence canpinpoint water quality problems.

• Improving the quality of watersupplies and preventing the casualuse of unprotected sources canalleviate the level of waterbornediseases in a community.

• The level of water-washed diseasesoccurring in a community can bereduced by increasing the amountof water available, improving theaccessibility and reliability ofsupply and improving hygiene.

• Water-based diseases can becombated by reducing the need forcontact with infected water,reducing levels of contaminationand controlling the aquatic vector.

• Water-related insect vectors can becontrolled by destroying breedingsites, reducing the need to visit sitesand implementing protectivemeasures.

• Holistic approaches to water-related disease problems arerequired.

• Hazard analysis can assist watersupply improvement programmesby identifying existing systemdeficiencies.rates on a day to daybasis.



Weaknesses

• Roof water is often contaminated bybird and animal excreta.

• Large uncovered areas of waterprovide breeding sites formosquitoes, and present adangerous situation where water-related diseases are endemic.

• Desalination, distillation, reverseosmosis and membrane filtrationare demanding and expensive hightechnology processes.

Strengths

• Run-off from roofs can be used tosupplement raw water sources, i.e.rainwater harvesting.

• Desalination, distillation, reverseosmosis and membrane filtration ofwater supplies are possible in areasprone to frequent shortages.

• Foul sewerage systems are capableof providing effective control ofwaste streams (thus protectingagainst infection) and feedingwastewater treatment facilities - toensure continuous operation.

• On-line wet waste systems includeseptic tanks and cess pits (withcollection/emptying services).

• Ventilated improved pit latrines andsimilar low technology wastecollection systems can limitexposure to pathogens, andprovide an effective means ofimproving public health.

6.6 Sewerage, special water sources and wastewater unit processes

References • 101

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Annex 1: Glossary • 105

Annex 1

Glossary

This glossary includes a few of the words and phrases commonly applied to watertreatment and environmental health. The explanations provided are thoserelevant to the context of this publication and may (in a few cases) deviate fromStandard English usage. In such cases, a technical dictionary should beconsulted. Conversely, for more specific explanations, an appropriate technicaldictionary should be used.

Abstraction The removal of water from a river or othersource for treatment in a water treatment works.

Activated Carbon A highly adsorbent form of carbon used toremove odours and toxic substances from liquidor gaseous emissions. In waste treatment it isused to remove dissolved organic matter fromwastewater.

Activated Sludge Product that results when primary effluent ismixed with bacteria-laden sludge and thenagitated and aerated to promote biologicaltreatment, speeding the breakdown of organicmatter in raw sewage undergoing secondarywaste treatment.

AIDS Acquired immuno-deficiency syndrome

Alum Aluminium sulphate (used as a coagulant)

Anaerobic Bacteria Bacteria that occur in, and are not destroyed by,the absence of oxygen.

Anoxic Not aerated

Antibiotic A microbial product which, in lowconcentrations, is capable of inhibiting or killingsusceptible microorganisms.

Aquiclude Impermeable stratum through whichgroundwater cannot penetrate.

Aquifer Water stored in strata above an aquiclude.

Assimilable Organic Carbon A measure of the carbon content of the water(AOC) which may be utilised by microorganisms for

growth.

Bacilli Any rod-shaped bacterial cell.

Bacterium A minute single celled organism which may beharmless or pathogenic.

BAT Best Available Technology

Bioaccumulative A substance with the potential to accumulatein biological organisms on prolonged exposure.

Biochemical Oxygen An indirect measure of the concentration of Demand (BOD) biologically degradable material present in

organic wastes. It usually reflects the amount ofoxygen consumed in five days by biologicalprocesses breaking down organic waste.

Biogrowth Biological growth

Biomass All of the living material in a given area; oftenrefers to vegetation.

Biota Living organisms

Biotic Indicators An organism, species or community whosecharacteristics show the presence ofenvironmental conditions.

Biotype A variant form of a given species,distinguishable by biochemical (metabolic) orother means.

Catchment Area Area from which all precipitation flows to asingle stream or set of streams.

Cholera In man, an acute infectious disease causes bythe cholerae or El Tor biotype of Vibriocholerae.

Chronic Disease Any disease which persists over a relatively longperiod (e.g. months or years).



Clarifier A tank in which solids settle to the bottom andare subsequently removed as sludge.

Coagulant A substance (usually aluminium or ferric salts)added in water treatment processes to causecoagulation followed by flocculation.

Coagulation Clumping of particles in wastewater to settle outimpurities, often induced by chemicals such aslime, alum and iron salts.

Cocci Any spherical or near spherical cell.

COCO DAFF™ Counter-current Dissolved AirFlotation/Filtration. A novel water treatmentflotation process. Microscopic bubbles areproduced in order to form a dense bubbleblanket, which assists in the removal of flocsfrom previously coagulated water.

Colloids Very small, finely divided solids (that do notdissolve) that remain dispersed in a liquid for along time due to their small size and electricalcharge.

Cryptosporidiosis Illness produced by infection withCryptosporidium.

DAF Dissolved Air Flotation

Denitrification The formation of gaseous nitrogen (and/oroxides of nitrogen) from nitrate (or nitrite) bycertain bacteria during nitrate respiration.

Desalination A drinking water treatment process involvingthe removal of salt from sea water.

Disinfectant Chemical agents used for disinfection.

Disinfection The destruction, inactivation or removal ofthose organisms likely to cause infection or togive rise to other undesirable effects.

Distillation Boiling water and collecting its condensate as ameans of water purification.

DNAPLs Dense Non-Aqueous Phase Liquids

DO Dissolved Oxygen

EA Environment Agency

EEC European Economic Community

Endemic Any disease which is commonly present in agiven geographical region.

Endotoxin Certain toxic substances within bacterial cells,which are released only on cell lysis.

Epidemic An outbreak of a given infectious disease inwhich, for a limited period of time, a highproportion of the population exhibits overtsymptoms of the disease.

Epidemiology The study of factors affecting health and diseasein populations, and the application of this studyto the control and prevention of disease.

Epilimnion The upper layer of water in a thermally stratifiedlake or reservoir. This layer consists of thewarmest water.

EU European Union

Exotoxins Proteins or proteinaceous toxins, which aresecreted by certain species of microorganisms.

Facultative Bacteria Bacteria that can live under aerobic oranaerobic conditions.

Faecal Indicator Microorganisms commonly found in faeceswhich, if detected in water, indicate that thewater has been faecally polluted.

Faecal-Oral Diseases Diseases spread by the contamination of foodor water by human faeces or urine.

Flagellum A thread-like appendage on a microbial cellusually associated with motility.

Floc A clump of solids formed in sewage bybiological or chemical action.

Flocculation Process by which clumps of solids in water orsewage aggregate through biological orchemical action, so they can be separated fromwater or sewage.

Flocculator Tank in which the flocculation process takesplace.

FOG Fats, Oils and Grease.



Free Residual Chlorine Chlorine remaining in water after the chlorinedemand has been satisfied.

Gastroenteritis Inflammation of the tissues of the stomach andintestine.

GDP Gross Domestic Product

Giardiasis Gastrointestinal disease caused by theprotozoan parasite Giardia lamblia.

GIS Geographic Information System

Granular Activated Carbon A filtering system often used in small water (GAC) Treatment systems and individual homes to remove

organics.

Groundwater Water contained in underground aquifers.

GV Guide Value

Hardness Characteristic of water caused by presence ofvarious salts. Hard water may interfere withsome industrial processes and prevent soapfrom lathering.

Helminth The scientific name for worm, i.e. multi-cellularorganism, which is generally longer than it iswide or deep.

Hypolimnion Bottom waters of a thermally stratified lake. Thehypolimnion of a eutrophic lake is usually lowor lacking in oxygen.

Immuno-competent When a person’s immune system is functioningproperly thus protecting them from disease.

Immuno-compromised When a person’s immune system is impaired,thus rendering them susceptible to disease.

Ion (e.g. Hypochlorite) A particle obtained by adding or removingelectrons from atoms or molecules. An atom ormolecule with missing electrons has a netpositive charge and is called a cation; one withextra electrons has a net negative charge and iscalled an anion.

Jar Tests Laboratory test performed in order to determinethe most suitable coagulant dose for a particularwater. Involves vigorous stirring of watersamples with a range of coagulant doses.

LNAPLs Light Non-Aqueous Phase Liquids

Malaria A disease of man and other animals caused bya species of Plasmodium (a protozoan), and isusually transmitted by the bite of a femaleAnopheles mosquito.

Membrane Filtration Membrane filtration uses a thin film of porouspolymer (plastic) as a filter media. This appliesto both reverse osmosis (RO) and nanofiltration(NF).

Microfungi Microscopic fungi

Microorganism An organism such as a bacterium, protozoan orvirus of microscopic size.

MLSS Mixed Liquor Suspended Solids

MSF Distillation Multistage Flash distillation

Nanofiltration A membrane treatment process which fallsbetween reverse osmosis and ultrafiltration onthe filtration/separation spectrum.

Neurotoxin A toxin which affects the nervous system.

Nitrification The process whereby ammonia in wastewater isoxidised to nitrite and then to nitrate bybacterial or chemical reactions.

NRA National Rivers Authority

NTU A unit of turbidity, established by a standardhaze created

(Nephelometric Turbidity chemically in water, and measured by anephelometric turbidimeter.Unit)

Oocyst The environmentally resistant transmissibleform of certain protozoa cryptosporidium,which is excreted in the faeces of an infectedhost.

ORT A weak solution of salts and sugar formulated torestore

(Oral Rehydration Therapy) lost electrolytes in patients with severe gastro-intestinal infections.

Oxidation The addition of oxygen that breaks down



organic waste or chemicals such as cyanides,phenols and organic sulphur compounds insewage by bacterial and chemical means.

Pandemic An outbreak of a disease that affects largenumbers of people in a major geographicalregion, or which has reached epidemicproportions, simultaneously, in many differentparts of the world.

Parasite An organism that lives on or in another (thehost) sometimes to the detriment of the host;and from which it obtains its nutrition.

Pathogenic A microorganism (bacterium, protozoan, virus)capable of causing disease.

Percolating Filters Biological wastewater treatment filter containinga bed of stone, on to which settled sewage isapplied and allowed to trickle through themedium’s interstices.

Pesticides Chemical agent applied to crops in order todestroy insects.

pH The concentration of hydrogen ions present.

Phreatic Surface A line of zero pore water pressure.

Plankton Tiny plants and animals that live in water.

Polyelectrolytes Long-chain polymers used as coagulant aids.

Potable Water fit for consumption.

Protozoan A single-celled microorganism, usually biggerthan a bacterium, which may be free-living orparasitic. Includes cryptosporidium and giardia.

Psittacosis An infectious disease caused by Chlamydiapsittaci, which is carried by parrots and otherbirds. This may cause atypical pneumonia whentransmitted to man.

RAS Returned Activated Sludge

RBCs Rotating circular discs providing a large surfacearea for

(Rotating Biological aerobic biological oxidation.Contactors)

Resistant Applied to an organism, which is able to survivedespite the presence of antibiotics.

RGF Rapid Gravity Sand Filter

RO (Reverse Osmosis) An advanced method of water or wastewatertreatment that relies on a semi-permeablemembrane to separate water from pollutants. Anexternal force is used to reverse the normalosmotic process, resulting in the solvent movingfrom a solution of higher concentration to oneof lower concentration.

Rotavirus A type of virus causing diarrhoea; mainly inchildren and young animals.

Schistosomiasis A water-based disease (also known asbilharzia). The causative agent is a worm, whichspends part of its life cycle within a particularspecies of snail.

Schmutzdecke Layer of bacteria and algal slime formed at thetop of a slow sand filter which contributes tofilter efficiency.

Serogroup Microorganisms grouped on the basis of theirreactions to antibodies.

Sludge Blanket Suspended layer of flocculated particles.

Softening The process of adding a substance, e.g. lime orsoda ash, to hard water in order to precipitateand remove the soluble hardness-causingcompounds. This is done in order to improvethe water’s suitability for washing and heatingpurposes.

Spore Resistant and/or disseminative forms producedasexually by certain bacteria.

SS Suspended Solids

SSF Slow Sand Filtration



THM (Trihalomethane) One of a family of organic compounds namedas derivative of methane. THMs are generallyby-products of chlorination of drinking waterthat contains organic material.

Vector Organisms which are involved in the spread ofdisease from one individual to another.

Viable Living

VIP Latrine Ventilated Improved Pit latrine.

Virulence Capacity of a pathogen to cause disease.

Virus A sub-microscopic organism of simple structurecapable of replication only within a living hostcell.

Waste Stabilisation Ponds Shallow ponds usually receiving raw sewage,which provide treatment by natural stabilisationprocesses.

Wastewater Water that has previously been used and is notpotable.

Waterborne Disease Disease spread by the contamination of waterby human faeces or urine.

WHO World Health Organization.

Zoogloeal Slime Slimy coating of sand in biologically active toplayer of SSF.

Chapter 6 Overview - Food and Agriculture Organization · Chapter 6: Overview • 91 Chapter 6...

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