Wastewater Treatment PDF

Wastewater Treatment  What is wastewater treatment O Usually refer to sewage treatment, or domestic wastewater treatment O process of removing contaminants from wastewater, both runoff and domestic  Goals O To produce waste stream (effluent) O To produce solid waste (sl...

Wastewater Treatment  What is wastewater treatment O Usually refer to sewage treatment, or domestic wastewater treatment O process of removing contaminants from wastewater, both runoff and domestic  Goals O To produce waste stream (effluent) O To produce solid waste (sludge) O To discharge or reuse them back into the environment  Where does wastewater come from? O Residences (kitchen, bathroom) O Commercial institution O Industrial institution (usually require specialized treatment process) How can it be treated? O Collected and transported via a network of pipes and pump stations to a municipal treatment plant  3 stages of water treatment O Primary O Solids are separated O Secondary O Dissolved biological matter is converted into a solid mass by using water-borne bacteria O 95% of the suspended molecules should be removed O Tertiary O Biological solids are neutralized and then disposed of, and treated water may be disinfected chemically or physically  Types of treatment O Mechanical treatment O Influx (Influent) O Removal of large objects O Removal of sand and grit O Primary Sedimentation O Biological treatment O Trickling bed filter O Activated sludge O Chemical treatment O Disinfection Preliminary treatment O Remove large objects O Ex: sticks, rags, toilet paper, tampons O Raked screen O Clog equipment in sewage treatment plant  Treatment stages - Primary treatment O Typical materials that are removed during primary treatment include O Fats, oils, and greases (aka FOG) O Sand, gravels and rocks (aka grit) O Larger settleable solids including human waste, and O Floating materials Methods used in primary treatment O Sand catcher O Remove sand and grit O Control wastewater velocity O Sand grit and stone settle O Keep suspended organic matter in water O Damage equipments in the remaining treatment stage O Landfill  Primary treatment O Primary Sedimentation Tank O Remove grease, oil O Fecal solid settle, floating material rise to the surface O Produce a homologous liquid for later biological treatment O Fecal sludge is pumped to the sludge treatment plant  Treatment stages - Secondary treatment O Degrade biological content (dissolved organic matter) of the sewage O Ex: human waste, food waste, soaps, detergent O Added bacteria and protozoa into sewage O 3 different approaches O Fixed film system O Suspended film system O Lagoon system  Three approaches O Fixed Film Systems O grow microorganisms on substrates such as rocks, sand or plastic O wastewater is spread over the substrate O Ex: Trickling filters, rotating biological contactors  Trickling filters bed O Spread wastewater over microorganism O made of coke (carbonised coal), limestone chips or specially fabricated plastic media O Optimize their thickness by insect or worm grazing  Suspended Film Systems O Suspended Film Systems O stir and suspend microorganisms in wastewater O settled out as a sludge O pumped back into the incoming wastewater O Ex: Activated sludge, extended aeration  Activated sludge O Mixed community of microorganisms O Both aerobic and anaerobic bacteria may exist O Biological floc is formed O In the aeration tank, aerobic microbes feed on dissolved organics and convert them into; Carbon dioxide Water and; Biomass O These microbes then aggregate together into structures called flocs. O Flocs contain live and dead microorganisms and products of microbial metabolism. O Correctly structured flocs are easily settled, enabling the separation of treated effluent from sludge. Physical components of activated sludge process O aeration tank O oxygen is introduced into the system O Aeration source O ensure that adequate oxygen is fed into the tank O provided pure oxygen or compressed air O Secondary clarifiers O activated-sludge solids separate from the surrounding wastewater O Activated sludge outflow line O Pump-activated sludge back to the aeration tank O Effluent outflow line O discharged effluent into the bay or tertiary treatment plant O Lagoon Systems O hold the waste water for several months O natural degradation of sewage O Usually, reeds are preferred  Treatment stages – Tertiary treatment O remove disease-causing organisms from wastewater O 3 different disinfection process O Chlorination O UV light radiation O Ozonation  Chlorination O Most common O Advantages: low cost & effective O Disadvantages: chlorine residue could be harmful to environment  UV light radiation O Damage the genetic structure of bacteria, viruses and other pathogens. O Advantages: no chemicals are used O water taste more natural O Disadvantages: high maintenance of the UV-lamp  Ozonation O Oxidized most pathogenic microorganisms O Advantages: safer than chlorination fewer disinfection by-product O Disadvantage: high cost What can effluent use for? O discharged into a stream, river, bay, lagoon or wetland O used for the irrigation of a golf course, green way or park O If it’s sufficiently clean, it can be used for groundwater recharge Advanced Treatment O Nitrogen removal O Ammonia (NH3) → nitrite (NO2-)→ nitrate (NO3-) O Phosphorous removal O Precipitation with iron or aluminium salt O Lead to eutrophication O May cause algal bloom  Sludge treatment O Primary sludge usually have strong odors O Secondary sludge have high concentration of microorganism O Goals of treatments are: O Reduce odors O Remove water reduce volume O Decompose organic matter O Untreated sludge are about 97 percent water O Settling can reduce about 92 to 96 percent of water O dried sludge is called a sludge cake  3 different sludge treatments O Aerobic digestion O Anaerobic digestion O Composting  Aerobic digestion O Bacterial process O Need oxygen O Consume organic matter O Convert into carbon dioxide (CO2)  Anaerobic digestion O Bacterial process O Do not require oxygen O Consume organic matter O Produce biogas, which can be used in generators for electricity  Composting O Aerobic process O Requires the correct mix of carbon, nitrogen, oxygen and water with sludge O Generate a large amount of heat  Sludge disposal O Superheat sludge and convert into small granules that are rich in nitrogen O Sell it to local farmer as fertilizer O Spread sludge cake on the field O Save landfill space Summary Questions