•         Waste water- liquid effluents derived from domestic sewage or industrial sources, cannot be disposed untreated to lakes, river and sea due to public health, recreational, economic reasons

•         contain both organic and inorganic materials, microorganisms play important role in removing organic components.

•         Proper wastewater treatment results in elimination of pathogen preventing them from entering the water supply

Levels of Sewage Treatment

•         Sewage treatment involve multistep process involving both physical and biological treatment steps.

•         Primary Treatment- consist of physical separations, sewage entering treatment pass through series of grates and screen to remove large objects, effluent allowed to settle for hours for sedimentation to occur, heavy load of nutrients still present, if dumped will pollute

•         Secondary Treatment- reduce organic load to acceptable level, (normally involving microbiological process- Anoxic Secondary Treatment Process) before releasing to waterways

•         Tertiary Treatment - complete method but not widely adopted, expensive. Involving a physiochemical process employing precipitation, filtration, and chlorination to sharply reduce levels of inorganic nutrient eg. Phosphate, Nitrate from final effluent. Wastewater from tertiary treatment free  from nutrient, unable to support extensive microbial growth.

Anoxic Secondary Treatment Processes

•         Complex series of digestive, fermentative bacterial reactions

•         efficiency of treatment is expressed as Biochemical Oxygen Demand (BOD)-measured amount of dissolved oxygen used by microorganisms

•         the higher level of oxidisable organic and inorganic material in wastewater, the higher BOD. Efficient wastewater treatment plant can remove 95% or > of initial BOD

•         degradation process carried out in large enclosed tanks sludge digestors or bioreactors

•         major products of anoxic sewage treatment- methane (collected or burned off/used as fuel for generator in treatment plant) and carbon dioxide.

Aerobic Secondary Treatment

•         Aerobic decomposition using trickling filter and activated sludge method -most common

•         wastewater sprayed onto trickling filter (2m crushed rock bed), liquid pass through slowly, organic matter adsorbs to rocks, microbial growth occur followed by complete mineralisation of organic matter-ammonia, CO2, nitrate, sulphate, phosphate.

•         Activated sludge process- wasterwater mixed and aerated, growth of slime-forming bacteria plus others forming flocs(substratum) where small animals and protozoa get attach. Process of oxidation similar to trickling filter.

Water Purification

•         Potable water (drinking )- requires removal of pathogens, decrease turbidity, eliminate taste and odour, reduce chemicals such as manganese  and iron

•         water from waterways pumped into sedimentation basin -turbidity settle on gravel, sand

•         send to coagulation basin - aluminium and iron containing chemical added to form floc trapping microorganisms absorb organic matter, sediment, removes from water then filtered through sand removing about 99% microorganisms

•         Chlorination(sodium or calcium hypochlorite or as a gas from pressurised tanks kills microorganisms within 30 minutes

•         water then pumped to storage tanks before supplying to consumers.