H. D. Stensel

Functionally relevant microorganisms to enhanced biological phosphorus removal performance at full-scale wastewater treatment plants in the United States

The abundance and relevance ofAccumulibacter phosphatis (presumed to be polyphosphate-accumulating organisms [PAOs]), Competibacter phosphatis (presumed to be glycogen-accumulating organisms [GAOs]), and tetrad-forming organisms (TFOs) to phosphorus removal performance at six full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants were investigated. Coexistence of various levels of candidate PAOs and GAOs were found at these facilities. Accumulibacter were found to be 5 to 20% of the total bacterial population, and Competibacter were 0 to 20% of the total bacteria population. The TFO abundance varied from nondetectable to dominant. Anaerobic phosphorus (P) release to acetate uptake ratios (P(rel)/HAc(up)) obtained from bench tests were correlated positively with the abundance ratio of Accumulibacter/(Competibacter +TFOs) and negatively with the abundance of (Competibacter +TFOs) for all plants except one, suggesting the relevance of these candidate organisms to EBPR processes. However, effluent phosphorus concentration, amount of phosphorus removed, and process stability in an EBPR system were not directly related to high PAO abundance or mutually exclusive with a high GAO fraction. The plant that had the lowest average effluent phosphorus and highest stability rating had the lowest P(rel)/HAc(up) and the most TFOs. Evaluation of full-scale EBPR performance data indicated that low effluent phosphorus concentration and high process stability are positively correlated with the influent readily biodegradable chemical oxygen demand-to-phosphorus ratio. A system-level carbon-distribution-based conceptual model is proposed for capturing the dynamic competition between PAOs and GAOs and their effect on an EBPR process, and the results from this study seem to support the model hypothesis.

Characteristics and fate of organic nitrogen in municipal biological nutrient removal wastewater treatment plants

The aim of this study was to investigate the occurrence and fate of colloidal and dissolved organic nitrogen (CON and DON) across biological nutrient removal (BNR) activated sludge bioreactors. Primary and secondary effluent total nitrogen (TN) measurements and component fractionation, CON and DON concentration profiles across BNR bioreactors, and laboratory batch experiments with the process mixed liquor were carried out at several full-scale BNR plants in northern Poland. The organic nitrogen (ON) components were divided into high CON, low CON, and DON based on sequential filtration through 1.2, 0.45 and 0.1 μm pore-size filters. The average influent DON(0.1 μm) (<0.1 μm) concentrations ranged from 1.1 g N/m(3) to 3.9 g N/m(3) and accounted for only 4-13% of total organic nitrogen. In the effluents, however, this contribution increased to 12-45% (the DON(0.1 μm) concentrations varied in a narrow range of 0.5-1.3 g N/m(3)). Conversions of ON inside the bioreactors were investigated in more detail in two largest plants, i.e. Gdansk (565,000 PE) and Gdynia (516,000 PE). Inside the two studied bioreactors, the largest reductions of the colloidal fraction were found to occur in the anaerobic and anoxic compartments, whereas an increase of DON(0.1 μm) concentrations was observed under aerobic conditions in the last compartment. Batch experiments with the process mixed liquor confirmed that DON(0.1 μm) was explicitly produced in the aerobic phase and significant amounts of ON were converted in the anoxic phase of the experiments.

Treatability and fate of various phosphorus fractions in different wastewater treatment processes.

The increasingly more stringent phosphorus (P) discharge limits, which are below the concentrations reliably achievable with currently available technologies, demand for better understanding of phosphorus removal mechanisms. This study investigated the compositional fractions of phosphorus (P) in various effluents as well as the efficacy of different levels of treatment processes for removing different fractions of P in wastewater. The results showed that BNR can effectively remove most fractions of P, with relatively higher efficiencies (>93%) towards bioavailable forms of P including soluble reactive P (sRP), particulate reactive P (pRP) portion and particulate acid hydrolysable P (pAHP) and, it showed relatively lower efficiency (78%) towards organic P. Soluble acid hydrolysable P (sAHP) was not effectively removed (<40%). Chemical P removal process was more effective for elimination of sRP, sAHP and particulate organic P (pOP), but was not as effective for removing pAHP and, it exhibited nearly no removal of dissolved organic P (DOP). We found that chemical P removal process led to a significant increase in the concentration of pRP by up to 255%, indicating that these pRP (presumably as chemically bounded P) are likely formed through chemical precipitation/co-adsorption. Only 22% and 64% of the pRP was removed through tertiary clarifier and filtration, respectively. This implies that chemical addition converts sRP into particulate-associated P, mostly as pRP that was not easily removed by sedimentation and filtration, therefore, the efficacy of chemical P removal highly depends on the effectiveness of solid and liquid separation process. As more sRP and particulate P were removed through the series of treatment processes, the percentage contribution from organic P increases with the level of treatment due to its recalcitrant nature. Our results indicated that in order to achieve extremely low effluent P levels, technologies and processes that can enhance pRP and DOP removal will be required.

A mechanistic model for fate and removal of estrogens in biological nutrient removal activated sludge systems

Two estrogen fate and transformation models were integrated with a comprehensive activated sludge model (ASM) to predict estrogen removal based on biomass and solids production. Model predictions were evaluated against published full-scale plant data as well as results from a laboratory-scale sequencing batch reactor (SBR) fed synthetic wastewater. The estrogen fate model relating the rate of total estrogen degradation to soluble estrogen concentrations successfully predicted estrogen removals when compared with measured concentrations. Model fit 17α-ethinylestradiol (EE2) biodegradation rate constant was 19 to 43% of the estrone (E1) value and 31 to 72% of the 17β-estradiol (E2) value.

Nitrogen transformations and mass balances in anaerobic/anoxic/aerobic batch experiments with full-scale biomasses from BNR activated sludge systems

The aim of this study was to investigate nitrogen mass balances occurring inside full-scale BNR activated sludge systems, with special attention to colloidal and dissolved organic nitrogen (CON and DON) transformations. For this purpose, laboratory experiments were carried out using process biomass from two large BNR plants in northern Poland. Two parallel batch reactors were operated in a 3-phase (anaerobic/anoxic/aerobic) cycle. In one reactor, the settled wastewater without any pretreatment was used, whereas the settled wastewater after coagulation-flocculation (to remove colloidal and particulate fractions) was added to another reactor. The chemical pretreatment of settled wastewater with ZnSO(4) did not adversely affect the observed nitrification rates in the (last) aerobic phase. It caused, however, a reduction of denitrification rates in the anoxic phase. Moreover, the chemical pretreatment did not appear to generally decrease DON but decreased CON. DON was explicitly produced in the aerobic phase and organic nitrogen conversion also occurred at a significant rate in the anoxic phase with biodegradable COD consumption and solids hydrolysis. The inorganic N mass balances revealed N losses up to approximately 10% which could be attributed to a few novel pathways of nitrogen removal, most likely aerobic denitrification or simultaneous nitrification/denitrification.

Estrogen nitration kinetics and implications for wastewater treatment.

Understanding estrogen-removal mechanisms in wastewater treatment is imperative, as estrogens have environmental effects at trace concentrations. Previous research investigating co-metabolic degradation of 17alpha-ethinylestradiol (EE2) by ammonia-oxidizing bacteria (AOB) revealed that, in batch tests where high nitrite-nitrogen (NO2-N) concentrations occurred as a result of ammonia-nitrogen (NH4-N) oxidation by AOB, an abiotic estrogen nitration reaction actually was occurring--not co-metabolic degradation. This paper addresses nitration kinetics. A first-order abiotic nitration model was developed that predicts nitration of EE2, 17beta-estradiol (E2), and estrone (El) as a function of temperature, pH, estrogen (EE2, E2, and E1), and NO2-N concentration. A contact time of 3.6 to 4.1 days is required for 90% estrogen nitration at 500 mg/L NO2-N and pH 6.4. At 20 degrees C and pH 6.4, the threshold NO2-N concentration for nitration to occur is 9 mg/L; therefore, estrogen nitration is not likely in activated sludge treatment of domestic wastewater, but has potential for high-NH4-N-strength wastewaters.

Monitoring the role of aceticlasts in anaerobic digestion: Activity and capacity

Aceticlastic methanogens are seen as a key to digester capacity and stability. This paper develops and applies an assay to measure digester stability by measuring the maximum aceticlastic methane production rate (Vmax,ac). The Vmax,ac in combination with acetate concentrations was found to be an effective digestion monitoring tool to indicate process upsets. At steady state, thermophilic, first stage and short SRT digesters generally had a greater Vmax,ac than mesophilic, second stage or long SRT digesters. The ratio of the Vmax,ac to the plant aceticlastic methane production rate, termed the Acetate Capacity Number (ACN), is a measure of the excess capacity of the digester. Either Vmax,ac or ACN can be used to estimate the capability to handle higher organic loading rates. Monod modeling was used to predict Vmax,ac, ACN and maximum VS loading rates for mesophilic and thermophilic digestion and for staged digesters to better understand expected digestion capacity and stability.

WERF Nutrient Challenge investigates limits of nutrient removal technologies.

The WERF Nutrient Challenge is a multi-year collaborative research initiative established in 2007 to develop and provide current information about wastewater treatment nutrients (specifically nitrogen and phosphorus in wastewater), their characteristics, and bioavailability in aquatic environments to help regulators make informed decisions. The Nutrient Challenge will also provide data on nutrient removal so that treatment facilities can select sustainable, cost-effective methods and technologies to meet permit limits. To meet these goals, the Nutrient Challenge has teamed with a wide array of utilities, agencies, consultants, universities and other researchers and practitioners to collaborate on projects that advance these goals. The Nutrient Challenge is focusing on a different approach to collaborating and leveraging resources (financial and intellectual) on research projects by targeting existing projects and research that correspond with its goals and funding those aspects that the Nutrient Challenge identified as a priority. Because the Nutrient Challenge is focused on collaboration, outreach is an absolutely necessary component of its effectiveness. Through workshops, webinars, a web portal and online compendium, published papers, and conference lectures, the Nutrient Challenge is both presenting important new information, and soliciting new partnerships.

A decentralized and onsite wastewater management course: bringing together global concerns and practical pedagogy

This paper reports on the design, implementation, and results of a course focused on decentralized and onsite wastewater treatment in global contexts. Problem-based learning was the primary pedagogical method, with which students tackled real-world problems and designed systems to meet the needs of diverse populations. Both learning and course evaluations demonstrated that the course was successful in fulfilling learning objectives, increasing student design skills, and raising awareness of global applications. Based on this experience a list of recommendations was created for co-developing and team-teaching multidisciplinary design courses. These recommendations include ideas for aligning student and teacher goals, overcoming barriers to effective group-work, and imbedding continuous course assessments.

Modeling the Methane and Toxic-Degradation Kinetics of Methane-Oxidizing Biofilm Reactors

The kinetics of methane-oxidizing bioreactors for the degradation of toxic organics are modeled. Calculations of the fluxes of methane and chlorinated hydrocarbons such as 1,1,1-trichloroethane (TCA) were made using biofilm model. The model simulates the effects of competition by toxics and methane on their enzymatic oxidation by the methane mono-oxygenase.