wastewater grade 1 exam Treatment updated 20-24/2025

wastewater grade 1 exam Treatment updated 20-24/2025 domestic wastewater Comes from schools, homes, hospitals, businesses, light industrial facilities. population equivalents 100 lbs wastewater per day, .2 lbs TSS/day, .17 BOD/day industrial wastewater Comes from industries. Compatible wastes can be processed by the plant. Incompatible wastes are toxic to the plant. sanitary wastewater The combined domestic and industrial waste waters from community. storm water Water that runs off roads, parking lots, and other impervious surfaces during rain and snow storms sanitary sewers Convey domestic and industrial waste waters, typically from where they are generated to the plant. storm sewers Convey storm water, typically from storm drains directly to a point of discharge (stream, river, ocean). combined sewers Convey sanitary waste water combined with storm water. Reasons to collect samples federal and state regulatory compliance, process control, trouble shooting, special studies including future designs. grab sample One time sample. Chlorine residual, coliform tests, settable solids, dissolved oxygen, pH, grease and oil, sulfide tests. Time based composite sample Fixed volume of sample is collected after passage of a set amount of time over a certain time period. Flow based composite sample Fixed volume of sample is collected after a prescribed amount of flow has passed through the sampling point, or a volume of sample proportional to the flow is collected after passage of a prescribed amount of time over a certain time period. This sample can also be called a flow proportional composite sample. diurnal flow Low at night between 2 and 5 am, steady steep increase in flow starting after 5 am, reaching first peak in the late morning or early afternoon, slight decrease through the afternoon, second peak between 6 and 9 pm, and a tapering off of to the low flows of 2 am. BOD Depletion of dissovled oxygen in a sample over 5 days at 20c is measured. Direct measure of the amount of dissolved oxygen consumed by aerobic bacteria over five days, indirect measure of the organic strength of waste water, used to asses the performance of WTP and the unit operations and unit processes used in WTP. COD This test involves the chemical oxidation of all organics in a sample. Measure of organic strength of waste water, COD is always greater than BOD, In raw municipal sewage COD is typically 2 to 4 times greater than BOD, takes 2 hrs to run COD compared to 5 days for BOD therefore more appropriate for process control. pH The log of the reciprocal of the the hydrogen ion concentration. PH 6 is 10 times the hydrogen ion concentration of 7. 5 is 100 times the conc of ph 7. Total solids TSS + TDS Settleable solids All settleable solids are TSS but not all TSS are settleable. Hydrogen sulfide h2s Toxic, flammable and explosive, rotten egg odor, dulls sense of smell, paralyzes ability to breath, corrosive, heavier than air collects in low lying areas. Methane ch4 Anaerobic digester have 62-70% methane vol basis. Lel is 5% and uel is 15%.flammable/ explosive. Odorless, not toxic but can asphyxiate at high conc, lighter than air. Anaerobic digester gas 65% methane, 34% carbon dioxide, 1% other inert gases. Contains less than 1% h2s Parshall flume Open channel device that constricts the flow in such away that the depth of flow upstream of the flume is directly related to the flow rate passing through the flume. Does not measure velocity. Carbon dioxide Aerobic bacteria exhale carbon dioxide. Anaerobic bacteria produce carbon dioxide. Non flammable, odorless, not toxic but can asphyxiate at high conc, heavier than air. Grit Sand, coffee grounds, seeds, small pieces of gravel and metals, eggshells. Removed by velocity controlled grit chambers or aerated grit chambers. Flow is slowed to 1 f/s Objectives of primary treatment Remove TSSset and the BOD associated with TSSset, remove floatable material(scum) Performance of primary clarifiers >95% SS removal, 40-60% TSS removal, 25-40% BOD removal, detention time 1.5 to 2.5 hrs, weir over flow 10000 to 15000 gal/d ft, hydraulic loading 600 to 1200 gal/d ft2 Hydraulic loading Gal/d ft2 (Surface loading or surface over flow rate) how many gallons of water per day are passing through each square foot of clarifier surface area. Performance is directly related to hydraulic loading . Weir overflow rate Gal/d ft. Divide flow in gal/ day by weir length in units of feet. Detention time Generally 1 hr minimum. If too long(2.5 -3hrs) then odors may be a problem in a primary clarifier and BOD removal may be compromised due to solubilization of BOD in the sludge blanket. Divide vol by influential flow rate. Primary clarifier performance The BOD and TSS tests should be run on 24hr, flow weighted primary influent and primary effluent composite samples. SS test should always be a grab sample. Anaerobic digestion Stabilization of raw sludge solids is the key. VS, pathogen, and volume reduction and gas production are the process objectives. Acid formers Converts part of the complex organic mixture in the influent sludge stream into volatile acids( organic acids) including acetic, propionic, and butyric acids Acetogenesis Formation of volatile acids Methane formers Convert volatile acids into ch4 and co2. Also called methanogenesis Buffer Prevents rapid changes in ph. Most buffer in healthy anaerobic digester is in the form of bicarbonate ion HCO3