Striking the balance between nutrient removal, greenhouse gas emissions, receiving water quality, and costs.

This Water Environment Research Foundation study considered the relationship between varying nutrient-removal levels at wastewater treatment plants, greenhouse gas emissions, receiving water quality (measured by potential algal production), and costs. The effluent nutrient concentrations required by some U.S. permits are very low, approaching the technology-best-achievable performance. This study evaluated five different treatment levels at a nominal 40 ML/d (10 mgd) flow. Greenhouse gas emissions and costs increase gradually up to the technologies' best-achievable performance, after which they increase exponentially. The gradual increase is attributed to additional biological treatment facilities, increased energy and chemical use, and additional tertiary nitrogen and phosphorus removal processes. Within the limited focus of this study, the evaluation shows that a point of diminishing return is reached as nutrient-removal objectives approach the technology-best-achievable performance, where greenhouse gas emissions and cost of treatment increases rapidly while the potential for algal growth reduce marginally.

WEF/WERF study of BNR plants achieving very low N and P limits: evaluation of technology performance and process reliability.

The Water Environment Research Foundation (WERF) funded a two-year comprehensive study of nutrient removal plants designed and operated to meet very low effluent total nitrogen (TN) and total phosphorus (TP) concentrations. WERF worked with the Water Environment Federation (WEF) to solicit participation of volunteers and provide a forum for information exchange at workshops at its annual conferences. Both existing and new technologies are being adapted to meet requirements that are as low as 3.0 mg/L TN and 0.1 mg/L TP, and there is a need to define their capabilities and reliabilities in the real world situation of wastewater treatment plants. A concern over very low daily permits for ammonia caused the work to be extended to include nitrification reliability. This effort focused on maximizing what can be learned from existing technologies in order to provide a database that will inform key decision makers about proper choices for both technologies and rationale bases for statistical permit writing. To this end, managers of 22 plants, 10 achieving low effluent TP, nine achieving low effluent TN, and three achieving low effluent NH(3)-N, provided three years of operational data that were analyzed using a consistent statistical approach. Technology Performance Statistics (TPSs) were developed as three separate values representing the ideal, median, and reliably achievable performance. Technological conclusions can be drawn from the study in terms of what can be learned by comparing the different nutrient removal and nitrification processes employed at these 22 plants.

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.

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.

Investigation and modeling of solar UV-induced chlorine decay in disinfection contact basins at full-scale wastewater treatment plants.

Residual chlorine loss due to UV sunlight in the chlorine disinfection contact basins (DCBs) was investigated at two full-scale wastewater treatment plants (WWTPs). Chlorine decay due to solar UV-induced photochemical reaction was found to be significant and had diurnal and seasonal variations. The total chlorine loss due to sunlight ranged from 19 to 26% of the total chlorine chemical use at the two plants studied. Covering chlorine contact basins led to more stable chlorine demand regardless of the diurnal and seasonal sunlight intensity. Therefore, covering chlorine contact basins offers more stable, or accurate, chlorine dosage and effluent residual control and requires less effort by plant operators. A mathematical model was developed to calculate the amount of UV-induced chlorine decay. The model developed can be used to estimate the UV-induced chlorine decay rate and total chlorine loss due to sunlight at WWTPs with various basin configurations, flowrates, chlorine dosages, and geographical locations. The model results allow the capital cost of covering needs to be assessed against the chlorine chemical cost savings.

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.

Kinetics and capacities of phosphorus sorption to tertiary stage wastewater alum solids, and process implications for achieving low-level phosphorus effluents.

The role of adsorption and/or complexation in removal of reactive or unreactive effluent phosphorus by already formed chemical precipitates or complexes has been investigated. Potential operational efficiency gains resulting from age of chemically precipitated tertiary alum sludge and the recycle of sludge to the process stream was undertaken at the Iowa Hill Water Reclamation Facility which employs the DensaDeg(®) process (IDI, Richmond, VA) for tertiary chemical P removal to achieve a filtered final effluent total phosphorus concentration of <30 µg/L. The effect of sludge solids age was found to be insignificant over the solids retention time (SRT) of 2-8 days, indicating that the solids were unaffected by the aging effects of decreasing porosity and surface acidity. The bulk of solids inventory was retained in the clarifier blanket, providing no advantage in P removal from increased solids inventory at higher SRTs. When solids recycle was redirected from the traditional location of the flocculation reactor to a point just prior to chemical addition in the chemical mixing reactor, lower effluent soluble P concentrations at lower molar doses of aluminum were achieved. At laboratory scale, the "spent" or "waste" chemical alum sludge from P removal showed high capacity and rapid kinetics for P sorption from real wastewater effluents. Saturation concentrations were in the range of 8-29 mg soluble reactive P/g solids. Higher saturation concentrations were found at higher temperatures. Alum sludge produced without a coagulant aid polymer had a much higher capacity for P sorption than polymer containing alum sludge. The adsorption reaction reached equilibrium in less than 10 min with 50% or greater removal within the first minute.

Struvite control through process and facility design as well as operation strategy.

Struvite deposition is a common problem in municipal wastewater treatment plants and can be significant if not anticipated, but struvite deposits are completely manageable if properly addressed. This paper summarises experiences from a number of facilities that have dealt successfully with struvite problems, elaborates on the interrelations between secondary treatment and anaerobic digestion, and outlines an approach to control struvite and available alternatives.