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Final Report: Enhanced Nutrient Removal from On-Site Wastewater Treatment Systems
EPA Grant Number: SU833545Title: Enhanced Nutrient Removal from On-Site Wastewater Treatment Systems
Investigators: Hu, Zhiqiang , Cole, Jamie , Liang, Zhihua , MaCulloch, Andrew , Nguyen, Huy , Thompson, Allen , Trauth, Kathleen M.
Institution: University of Missouri - Columbia
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: August 30, 2007 through August 29, 2008
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity, and the Planet (2007)
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Water
Description:
Objective:Nutrient (nitrogen and phosphorus) runoffs impact streams and ecosystems. On-site wastewater treatment systems are important sources of nutrient discharges because effluents from septic tanks typically contain high concentrations of organic matter, nitrogen and phosphorus. It is urgent to develop cost-effective and efficient environmental technologies to remove the nutrients from septic systems.
The research objective of this interdisciplinary student team is to develop a membrane aerated reactor system for efficient nitrogen and phosphorus removal from domestic wastewater. In this research, a gas-permeable membrane was applied as a carrier for aeration and nitrifying biofilm formation, and further, metallic iron materials was introduced in anoxic basins to promote abiotic denitrification and chemical phosphorus precipitation. We explored the limits of technology (LOT) for nutrient removal by characterizing attainable effluent nutrient concentrations and will develop a scaled-up membrane-aerated modular unit for pilot testing.
Summary/Accomplishments (Outputs/Outcomes):The MU P3 team developed a prototype of membrane-aerated modular unit as a key measurable output. This P3 project also presented an experimentally validated procedure to start-up and operate the lab-scale MABR system that will be scaled up for on-site wastewater treatment testingat the Massachusetts Alternative Septic System Test Center.
The student team has built a bench scale bioreactor with an operating volume of ~7L. The reactor consists of three compartments: an anaerobic fermentation basin followed by an anoxic basin, and further followed by an internal clarifier. In the anoxic basin, an aerated membrane module covered by steel wools will be submerged. The reactor is operated under constant hydraulic retention time (target HRT = 3 d), SRT (target SRTtotal >100 d, and SRTanaerobic > 50 d). A nitrifying enrichment culture (collected in the lab previously) and activated sludge from the Columbia Wastewater Treatment Plant (Columbia, MO) was used as inocula. For laboratory process optimization only, pure oxygen was provided for aeration.
A gas permeable membrane support was constructed for immobilization of nitrifying bacteria and immersed in the bulk volume (Figure 1). The support consists of a gas-permeable membrane (Silastic® medical grade tubing, outer diameter = 2.0 mm and inner diameter =1.4 mm, Dow Corning, active length = 10 m), the inner and outer sides of which were covered with a polypropylene nonwoven material (diameter = 10 μm) to enhance the formation of nitrifying biofilm. Oxygen was supplied to the inside of the membrane tube at an airflow rate of ~2 ml/min.
The feed medium was designed to represent domestic wastewater, which contains the following (per liter of deionized water): 0.6 g sodium acetate, 0.1 g ammonium chloride, 0.28 g sodium phosphate, and the required macro/micro nutrients (details in Attachment). The medium has an average chemical oxygen demand (COD) of approximately 470 mg/L, NH4+-N of 30 mg/L and TP of 6 mg/L. Nitrogen species, phosphorous and chemical oxygen demand (COD) were determined colorimetrically according to standard methods [APHA, 1998 #182].
For parallel comparison, the MU P3 team also runs a microbial fuel cell (MFC) based bioreactor with baffled chambers to evaluate the nutrient removal efficiency. The baffles were designed such that the MFC system mimics traditional on-site wastewater treatment systems with internal settling zones. The anode and cathode were placed on opposite sides of the MFC-based reactor and connected with an external circuit (~ 1000 Ω resistor). Both the anode and cathode were made of carbon paper (effective total area of 1800 cm2, Toray™ Carbon, E-TEK, NJ, USA). Room air was provided adjacent to the cathode to provide O2 as the electron acceptor (details in attachment).
COD and NH4+-N were efficiently removed in both reactors. In the membrane aerated biofilm reactor, the initial average influent COD was maintained for about 2 weeks at 202 ± 28 mg/L and the average effluent COD was 26 ± 9 mg/L, a 87% removal after the treatment. The influent COD was increased to 340 ± 39 mg/L from day 28 onward and the average effluent COD was 55 ± 14 mg/L, with an overall removal efficiency of 84% after the treatment.
NH4+-N was removed in a similar pattern, with typical effluent NH4+-N concentrations less than 1 mg/L and an average removal rate of 93% throughout the MABR system. There was little nitrite (< 1 mg/L) accumulated during the MABR treatment. The average effluent NO2- -N concentration from the last two weeks was 0.3 mg/L. However, significant nitrate accumulation was observed during the start-up operation. The effluent NO3- -N concentration was 17 ± 7 mg/L from day 16 to day 23, largely because of the uncontrolled membrane aeration to cause the prevalence of aerobic environment throughout the MABR system. After day 28, the aeration rate was controlled to about ~2 mL/min, nitrate removal was considerably improved and the average effluent NO3- -N concentration was below detection limit. The effluent total N concentrations after MABR treatment were 2.1 mg/L indicating overall efficient nutrient removal in MABR systems.
The average influent and effluent phosphorous concentrations, however, were 6 and 5.1 mg/L respectively, indicating low biological phosphorous removal with existing treatment systems.
The membrane aerated modular unit is ready for field testing at the Massachusetts Alternative Septic System Test Center. Realizing the significant environmental impact of on-site wastewater treatment systems on environmental sustainability, both developing and developed countries continue to seek innovative treatment systems and management options to reduce or eliminate nutrient contamination from septic systems. The phase I results achieved by the MU P3 team will help to develop full scale modular products for large scale applications to protect the environment and the public health.
Conclusions:The MU P3 team developed a prototype of membrane-aerated modular unit that can be scaled up for on-site wastewater treatment testingat the Massachusetts Alternative Septic System Test Center.
Proposed Phase II Objectives and Strategies:
Built on the successful development of laboratory scale membrane-aerated modular unit, the objective of the MU P3 phase II project is to develop a scaled-up membrane aerated biofilm reactor system and to test the field efficiency of nitrogen and phosphorus removal from domestic wastewater. Specifically, the proposed research will: (1) develop a scaled-up membrane-aerated modular unit for pilot study at the Massachusetts Alternative Septic System Test Center and (2) explore the limits of technology (LOT) for nutrient removal by characterizing attainable effluent N and P concentrations and end products of abiotic/biotic processes.
The student team will build a scaled-up (1:500) membrane modular unit to be used in a 1000 gal two-compartment septic tank. The MU P3 team will prefabricate the scaled-up membrane modular unit before testing. A gas permeable membrane support will be constructed for immobilization of nitrifying bacteria and immersed in the bulk volume. The support consists of a gas-permeable membrane (Silastic® medical grade tubing, outer diameter = 2.0 mm and inner diameter =1.4 mm, Dow Corning, active length = 500 m), the inner and outer sides of which will be covered with a polypropylene nonwoven material (diameter = 10 μm) to enhance the formation of nitrifying biofilm. Enriched nitrifying suspension will be applied to the membrane modular unit for inoculation purposes before the septic tank is fed with real wastewater. Oxygen will be supplied to the inside of the membrane tube at an adjustable airflow rate of up to 40 L/min. using a 40-watt Hakko linear air pump.
To explore the limits of technology (LOT) for nutrient removal by characterizing attainable effluent N and P concentrations, the period of testing will consist of a approximately four-week startup period, and a twelve-month testing period incorporating several stress periods to simulate real household conditions. The testing facility at the Massachusetts Alternative Septic System Test Center will dose real wastewater at a rate of 100% of their rated capacity using a daily flow-pattern that mimics the generation of wastewater in a residence. According to a previous report, the average influent wastewater characteristics are as follows: BOD5 = 181 mg/L; TSS = 159 mg/L; Total Nitrogen = 34.4 mg/L; alkalinity = 168 mg/L; pH = 7.37. TP was assumed to be 6-10 mg/L. Volumetric doses will be controlled by a programmable logic controller, and occur in 15 equal dosing events of approximately 27 gallons per dose.
The influent flow (= 250 gal/day) with targeted HRT of 4 d will be through the use of timed pump operation and will conform to the following pattern as representative of a typical residence(s) scenario:
6 a.m. – 9 a.m. approximately 33% of total daily flow in 5 doses
11 a.m. – 2 p.m. approximately 27% of total daily flow in 4 doses
5 p.m. – 8 p.m. approximately 40% of total daily flow in 6 doses
Wash-day stress simulation will be considered during the pilot test. The simulation will consist of three wash-days in a five day period with each washday separated by a 24-hour period. During a wash-day, in addition to receiving the normal flow pattern, during the course of the first two (2) dosing periods per day, the hydraulic loading will include two wash loads [two wash cycles and four rinse cycles] with added hydraulic loading rate of 180 gal/d (~30 gallons per cycle). Common (readily available to consumers) detergent and non-chlorine bleach will be added to each wash load.
The developed membrane-aerated modular unit at an affordable price will be readily adapted for use in septic tanks so that the concern for operation, maintenance, and process control of sophisticated technology can be largely eliminated. The minimum amount of iron-enriched sludge generated in the systems will immobilize the phosphorus, and thus making the residue suitable for land application while minimizing nutrient leaching into groundwater or runoff into streams and ecosystems. It is anticipated that people in both developed and developing countries have the potential to gain a double benefit by simultaneously capturing valued products (P-rich sludge as a fertilizer) and reducing pollutant (e.g., ammonia, phosphate, and methane) emissions. The development of this largely passive technology will also provide excellent training and service learning opportunities in wastewater treatment and sustainable environment for the participating students.
Journal Articles:No journal articles submitted with this report: View all 1 publications for this project
Supplemental Keywords:waste reduction, wastewater treatment, nutrient removal, treatment/control, engineering, clean technologies, environmental engineering, innovative technology, environmental chemistry, biotechnology, adsorption, community-based, sustainable environment, green chemistry,
Relevant Websites:
http://web.missouri.edu/~huzh/EPAP3project.htm 
Progress and Final Reports:
Original Abstract