1. Intake with screen removes floating, large solid impurities. The removed solids are called screenings, and they are treated and disposed as solid wastes. Mixing tank is where coagulants such as alum, aluminium sulfate, ferric chloride, ferrous sulfate or lime are mixed with raw water (Al-Najar), there is no waste stream generated from mixing tank since the process is quick and there is no time to settle. In, the flocculator slow mixing occurs to allows for floc formation, the chemicals added in mixing tank promote this process. Flocculated suspended impurities settle sooner due to their large size and mass. Hence, in settling tank, during retention the flocs (suspended impurities) are removed. Sludge from the bottom of settling tank is the waste stream, it contains chemicals added during mixing. Dual media filter with sand and anthracite or other media is used to further remove smaller suspended particles about 10-20 micron size, odor and color from the clarified water (Chemtronics). Filter wash water used to clean the beds is the waste stream generated.
2. There is no mention of nitrogen or phosphorus compounds in the effluent, so it may not be required. The effluent treatment plant components required are listed below in order.
3. In preliminary treatment floating solids are removed and settling solids of large particle size are removed in primary settling. During biological treatment and secondary settling remaining organics (BOD) and suspended solids are removed and disinfection removes pathogenic microbes. For discharge into lake, nutrients such as nitrogen and phosphorus compounds have to be removed from the wastewater to prevent eutrophication. So, a nitrification/de-nitrification step, and phosphorus removal system may be needed if nitrogen or phosphorus content is above discharge limits. For discharge into underground aquifer suspended solids have to be removed further, to prevent any clogging and septicity in soil (FAO). Hence, a filter can be installed after secondary treatment i.e. BOD removal. Since domestic sewage will have less or no heavy metals no additional treatment may be required for discharge into aquifer.
4. Domestic rainwater harvesting systems can be encouraged, and developing proper sanitation systems, and preventing runoff must improve existing surface water quality (WHO). Quality of water bodies must be periodically checked to ensure the contamination level. Constructing or renovating and water/sewage treatment plants might take some time and need investment, but cleaning existing catchments and reservoirs would be cost effective. These steps can improve access to safe water in Haiti.
Works Cited
Al-Najar, Husam. "Lecture 5: Coagulation and Flocculation." 2010. Web. 26 May 2016.
<http://site.iugaza.edu.ps/halnajar/files/2010/09/Lecture-5.-Coagulation-and-Flocculation.pdf>.
Chemtronics. "Dual Media Filter." Web. 26 May 2016. <http://www.chemtronicsindia.com/
dual-media-filter.htm>.
FAO. "Aquifer Recharge with Wastewater." Web. 26 May 2016. <http://www.fao.org/
docrep/t0551e/t0551e06.htm>.
WHO. "JMP Thematic Report on Drinking Water 2011." 2011. Web. 26 May 2016.
<http://www.wssinfo.org/fileadmin/user_upload/resources/report_wash_low.pdf>
