Water Treatment Plan

WATER TREATMENT PLAN

Section Key points OHP

Introduction -need to treat all surface waters and some groundwaters contamination may be microbiological, chemical or physical microbiological contamination is most important as it causes highly infectious disease with short-term impacts chemical contamination tends to have longer term effects on health suspended solids affect microbial survival and the acceptability of water always disinfect water supplies and maintain a residual in the water for protection against contamination during distribution and storage

Multiple Barrier Principle

need to have more than a single process during treatment prevents breakdown in one process leading to complete treatment failure source must be well protected

Treatment processes

many processes available, the suitability of each is a function of source quality, operator capacity and financial resources technology selection must be made on the basis of the above to ensure sustainability often need to reduce turbidity before treating water as this may interfere with treatment prefiltration is a physical process which removes suspended solids prefilters can be horizontal, vertical upflow or vertical upflow-downflow main advantage is limited working parts and doesn't use chemicals disadvantages include poor ability to remove fine material, microbial removal poor and may need frequent cleaning sedimentation is achieved by the settling of particles in slow moving water simple sedimenters do not use chemical coagulants and are not effective in removing fine material

Section Key Points OHP

Settling is improved through addition of coagulants to form larger aggregates which speeds up settling and removes fine material

modular and plate settlers improve settling efficiency

alum is the most common coagulant, others include

polyelectrolytes and ferric salts such as sulphate and

chloride

Advantages include removal of fine particles, removal of some viruses, quick, compact disadvantages include expense, need for good monitoring capacity, need trained operators

Sand filtration can be rapid or slow

Slow sand filtration is a biological process and rapid sand

filtration a physical process

Slow sand filters a biologically active top layer called the schumtzdecke which is composed of predatory bacteria

Schumtzdecke kills bacteria and viruses

Require cleaning @ every 2 months, take 3-4 days to recover

Rapid sand filters work at much faster rates and remove suspended solids

Advantages of slow sand filtration include production of good quality water, relatively simple to operate

Disadvantages include large land requirement, labour intensive, requires low turbidity water

Advantages of rapid sand filtration include small land requirement