116 Nutrient Removal Project The nutrient removal project is an opportunity to synthesize what you have learned about environmental engineering and to learn about process control, real time data analysis, and the design and operation of a simple wastewater treatment plant. This project will span several weeks during which time a team of students will select a treatment process, approximate the process using a sequencing batch reactor, develop the control algorithms for automation, operate the plant for several weeks, and monitor the plant performance. Project Milestones · Measure oxygen transfer efficiency with clean water (Gas Transfer Experiment). · Select a reactor type (10 cm diameter cylinder or rectangular tank). · Select a reactor process that can be carried out in a single sequencing batch reactor (SBR). · Convert the process from a continuous flow reactor into a SBR so it can be modeled in a single reactor. · Write and test the control logic to automate the SBR (fill, aerate, settle, waste, etc.). · Test the operation of the SBR using tap water. · Begin treating the synthetic waste. Use activated sludge to get the treatment process jump-started. · Frequently measure the volatile suspended solids using the gravimetric technique to verify that the reactor system is maintaining a healthy community of microbes. Research Options 1) Develop an algorithm to control the dissolved oxygen concentration in the SBR. Compare the ability of several different control algorithms. Log the relevant parameters to a file for analysis. 2) Research algorithms used to control a process (see Dissolved Oxygen Control on page 125). Develop an algorithm to automate the measurement of the oxygen uptake rate. Measure the oxygen uptake rate periodically and generate a graph containing the uptake rate as a function of time. Log the measured oxygen uptake rate to file. 3) Research biological phosphorus removal techniques. Operate the plant to optimize phosphorus removal and measure phosphorus removal (See Phosphorus on page 131). Note that phosphorus measurements are done using a colorimetric wet chemistry technique that we can’t easily automate. 4) Develop a control strategy to maintain a desired level of volatile suspended solids in the SBR. Consider using the Honeywell turbidity sensors or the Hach turbidimeter to automatically measure the turbidity and use the turbidity measurement to estimate the volatile suspended solids. CEE 453: Laboratory Research in Environmental Engineering Spring 2003117 Reactor Specifications Each team will use a single reactor for the wastewater treatment plant. The maximum reactor volume will be 4 L. Aeration will be provided using a solenoid valve and accumulator to meter air from the laboratory low-pressure air supply. A magnetic stirrer will mix the reactor contents and will be controlled (on and off) by the NRP software. Reactor Designs for Denitrification The following reactor designs are from (Rittmann and McCarty 2001). Tertiary Denitrification using Activated Sludge Solids Retention Time, SRT, of 5 d High cell concentration increases reaction rate Electron donorNo aeration!Solids recycle3NO-2N Biofilm Processes Submerged fixed beds of rocks, sand, limestone, or plastic media Fluidized beds of sand, activated carbon, and pellets of ion-exchange resin Circulating beds of a range of lightweight particles Membrane bioreactors (membrane supplies H2 and is the attachment surface) HRT can be less than 10 minutes! Biomass storage and decay Uses biomass as electron donor for denitrification Slow kinetics of endogenous decay BOD0TKN03NO-Biomass2N2COSludge recycleSludge wasteLow BOD0Low3NO-4NH+Some Nutrient Removal Project118 Classical pre-denitrification Uses BOD as electron donor for denitrification Requires high mixed liquor recycle (4Qplant) Sludge recycleSludge wasteBOD0TKN02COSome BODLow3NO-4NH+Some4NH+Low BOD3NO-2NMixed liquor recycle Simultaneous nitrification with denitrification Uses BOD as electron donor Low oxygen levels permit denitrification BOD0TKN03NO-4, andNH+Low BOD,Sludge recycleSludge waste Barnard Process Greater than 90% removal of TKN! Sludge recycleSludge wasteBOD0TKN02COSome BODLow3NO-4NH+Some4NH+Low BOD3NO-2N4NH+3 h11 h1 h2N3 h Sequencing Batch Reactor Same process as Barnard carried out in a single tank CEE 453: Laboratory Research in Environmental Engineering Spring 2003119 BOD0TKN02CO3NO-2N3 h 3 h 2 h 0.33 h 0.67 h2N3NO-BOD0TKN03NO-Biomass3NO-4NH+3NO- Feed Composition The feed composition is based on a synthetic feed used by (Cicek, Franco et al. 1998). The feed was divided into 3 stock solutions to simplify preparation. The inorganic stocks (Stocks 2 and 3) will be added to tap water in a 100 L tank that will be pumped to each plant. Stock 1, containing the biodegradable organics, will need to be refrigerated. Stock 1 will be diluted to a 20x stock and will be stored in a small container in a refrigerator located near the sequencing reactor. The diluted organic stock will be metered into the plant by gravity. The amount of stock metered into the plant will be controlled by either measuring the pressure at the bottom of the stock bottle or by measuring the increase in pressure in the sequencing batch reactor. The advantages of using a slightly more dilute organic stock are that more of the starch is soluble and that it is easier to measure the volume of the organic stock that must be added to the sequencing batch reactor. The compositions of the 3 stock solutions are given in Tables 10-1 to 10-3. Table 10-1. Composition of synthetic feed stock 1. Compound Chemical Formula Molecular Weight Concentration Stock Concentration (100x) g/mol mg/L g/L Starch ~40,00084.40 8.440Casein ~30,000125.00 12.500Sodium acetate C2H3O2Na3H20 136.1 31.90 3.190Capric acid C10H20O2172.3 11.60 1.160Ammonium chloride NH4Cl 53.5 75.33 7.533Potassium phosphate K2HPO4174.2 6.90 0.690Sodium hydroxide NaOH 40.0 175.00 17.500Glycerol C3H8O392.1 12.00 1.200 Nutrient Removal Project120 Table 10-2. Composition of synthetic feed stock 2. Compound Chemical Formula Molecular Weight Concentration Stock Concentration (1000x) g/mol mg/L g/L Magnesium sulfate MgSO47H2O 246.5 69.60 69.600Sodium molybdate NaMoO42H2O 241.9 0.15 0.150Manganese sulfate MnSO4H2O 169.0 0.13 0.130Cupric sulfate CuSO44H2O 249.7 0.08 0.080Zinc suflate ZnSO47H2O 287.5 0.48 0.480 Table 10-3. Composition of synthetic feed stock 3. Compound