Charles Bott

High-rate activated sludge system for carbon management – Evaluation of crucial process mechanisms and design parameters

The high-rate activated sludge (HRAS) process is a technology suitable for the removal and redirection of organics from wastewater to energy generating processes in an efficient manner. A HRAS pilot plant was operated under controlled conditions resulting in concentrating the influent particulate, colloidal, and soluble COD to a waste solids stream with minimal energy input by maximizing sludge production, bacterial storage, and bioflocculation. The impact of important process parameters such as solids retention time (SRT), hydraulic residence time (HRT) and dissolved oxygen (DO) levels on the performance of a HRAS system was demonstrated in a pilot study. The results showed that maximum removal efficiencies of soluble COD were reached at a DO > 0.3 mg O2/L, SRT > 0.5 days and HRT > 15 min which indicates that minimizing the oxidation of the soluble COD in the high-rate activated sludge process is difficult. The study of DO, SRT and HRT exhibited high degree of impact on the colloidal and particulate COD removal. Thus, more attention should be focused on controlling the removal of these COD fractions. Colloidal COD removal plateaued at a DO > 0.7 mg O2/L, SRT > 1.5 days and HRT > 30 min, similar to particulate COD removal. Concurrent increase in extracellular polymers (EPS) production in the reactor and the association of particulate and colloidal material into sludge flocs (bioflocculation) indicated carbon capture by biomass. The SRT impacted the overall mass and energy balance of the high-rate process indicating that at low SRT conditions, lower COD mineralization or loss of COD content occurred. In addition, the lower SRT conditions resulted in higher sludge yields and higher COD content in the WAS.

Nitrogen removal assessment through nitrification rates and media biofilm accumulation in an IFAS process demonstration study.

An IFAS demonstration study was conducted at the 76,000 m(3)/day (20MGD) James River Wastewater Treatment Plant (JRTP) located in Newport News, Virginia by converting one fully-aerobic conventional aeration basin with dedicated secondary clarification to a 7041 m(3)/day (8404 m(3)/day max month) IFAS train in a modified Ludzack-Ettinger (MLE) configuration. During the study, biomass concentrations on the biofilm carriers were monitored (weekly) as well as nitrogen species concentrations in the IFAS reactor to quantify the nitrogen transformations occurring within the demonstration tank. In a related effort, nitrification kinetics for ammonia and nitrite oxidizing bacteria were monitored on a weekly basis for IFAS media alone, IFAS process mixed liquor without media, and IFAS mixed liquor and media together in an effort to identify the location of nitrification activity (i.e. on the media or in the suspended culture) in the IFAS process. Biomass quantity on the media was generally observed to be inversely related to temperature except during a period when an auxiliary carbon source contaminated with fungi was introduced. Both ammonia oxidizing and nitrite oxidizing bacterial activity were elevated on the carriers compared to the suspended culture (AOB(media): 4.97 mgNOx/gMLSS/hr; AOB(suspended): 1.72 mgNOx/gMLSS/hr; NOB(media): 7.55 mgNOx/gMLSS/hr; NOB(suspended): 0.82 mgNOx/gMLSS/hr) during all periods of the study. In-basin nitrification rates calculated based on nitrogen profiling efforts averaged 0.90 mgNOx/m(2)/day which was in good agreement with the average of 0.89 mgNOx/m(2)/day for IFAS mixed liquor and media from batch testing.

The immunochemical detection of stress proteins in activated sludge exposed to toxic chemicals

The heat shock protein, GroEL, was found to be induced in activated sludge cultures exposed to perturbations of chemicals (cadmium, pentachlorophenol, and acetone) or heat stress. In laboratory activated sludge reactors, GroEL was rapidly induced (within minutes) in the presence of 5 mg/l or greater total cadmium. At 5 mg/l cadmium, however, moderate to insignificant changes in activated sludge process performance indicators [effluent suspended solids concentration, chemical oxygen demand (COD) removal, and specific oxygen uptake rate] were observed. As total cadmium concentrations increased above 5 mg/l, there was a significant and consistent increase in effluent volatile suspended solids concentrations from activated sludge sequencing batch reactors relative to unstressed controls. These results indicate that stress proteins may serve as sensitive and rapid indicators of mixed liquor toxicity which can adversely impact treatment process performance, but that GroEL may not be a good candidate protein for this purpose.

Characterizing denitrification kinetics at cold temperature using various carbon sources in lab-scale sequencing batch reactors.

Wastewater treatment plants in the Chesapeake Bay region are becoming more interested in external carbon sources for denitrification. This is in response to the recent regulations to remediate the Chesapeake Bay, which will limit effluent total nitrogen to near 3 mg/L for plants, thus requiring near complete elimination of inorganic nitrogen species. Since sufficient internal carbon is usually not available for complete denitrification, external carbon is needed to supplement internal sources. Of particular interest is the use of an alternate external carbon source to replace the least expensive source methanol. This study focuses on three commonly available external carbon sources: methanol, ethanol and acetate. The aim of this study was to obtain the specific denitrification rate (SDNR) of the substrates under several conditions. Sequencing batch reactors (SBRs) were set up to first grow biomass to the specified substrate while in situ SDNRs were conducted concurrently. Once the biomass was grown with the corresponding substrate, a series of ex situ SDNRs were performed using various biomass/substrate combinations to evaluate response to substrate combinations at 13 degrees C. Results from this study indicate that the SDNRs for biomass grown on methanol, ethanol and acetate were 9.2 mg NO(3)-N/g VSS/hr, 30.4 mg NO(3)-N/gVSS/hr and 31.7 mg NO(3)-N/g VSS/hr, respectively, suggesting that acetate and ethanol were equally effective external carbon sources followed by much lower SDNR using methanol. Ethanol could be used with methanol biomass with similar rates as that of methanol. Additionally, methanol was rapidly acclimated to ethanol grown biomass suggesting that the two substrates could be interchanged to grow respective populations with a minimum lag period.

Implicating the Glutathione-Gated Potassium Efflux System as a Cause of Electrophile-Induced Activated Sludge Deflocculation

ABSTRACT The glutathione-gated K+ efflux (GGKE) system represents a protective microbial stress response that is activated by electrophilic or thiol-reactive stressors. It was hypothesized that efflux of cytoplasmic K+ occurs in activated sludge communities in response to shock loads of industrially relevant electrophilic chemicals and results in significant deflocculation. Novosphingobium capsulatum, a bacterium consistent with others found in activated sludge treatment systems, responded to electrophilic thiol reactants with rapid efflux of up to 80% of its cytoplasmic K+ pool. Furthermore, N. capsulatum and activated sludge cultures exhibited dynamic efflux-uptake-efflux responses very similar to those observed by others in Escherichia coli K-12 exposed to the electrophilic stressors N-ethylmaleimide and 1-chloro-2,4-dinitrobenzene and the reducing agent dithiothreitol. Fluorescent LIVE/DEAD stains were used to show that cell lysis was not the cause of electrophile-induced K+ efflux. Nigericin was used to artificially stimulate K+ efflux from N. capsulatum and activated sludge cultures as a comparison to electrophile-induced K+ efflux and showed that cytoplasmic K+ efflux by both means corresponded with activated sludge deflocculation. These results parallel those of previous studies with pure cultures in which GGKE was shown to cause cytoplasmic K+ efflux and implicate the GGKE system as a probable causal mechanism for electrophile-induced, activated sludge deflocculation. Calculations support the notion that shock loads of electrophilic chemicals result in very high K+ concentrations within the activated sludge floc structure, and these K+ levels are comparable to that which caused deflocculation by external (nonphysiological) KCl addition.

Balancing yield, kinetics and cost for three external carbon sources used for suspended growth post-denitrification.

Facilities across North America are designing plants to meet stringent limit of technology (LOT) treatment for nitrogen removal. In the Mid-Atlantic region of the United States, this is in response to the Chesapeake Bay Agreement, which limit effluent total nitrogen discharges from wastewater treatment plants to between 3-5 mg/L. Since denitrification is crucial for the removal of nitrogen, maximizing this process step will result in a decrease in nutrient load to the receiving waters. Of particular interest is the use of an alternate external carbon source to replace the most commonly used carbon, methanol. Three external carbon sources were evaluated in this study including: methanol, ethanol and acetate at 13 degrees C. The aim of this study was to evaluate the relative benefits and constraints for using these three carbon types. Laboratory scale Sequencing Batch Reactors (SBRs) were set up to grow and acclimate carbon free biomass to the specified substrate while in-situ Specific Denitrification Rates (SDNRs) were conducted concurrently. The results suggest that the SDNRs for acetate (31.0 + or - 4.6 mgNO(3)-N/gVSS/hr) and ethanol (29.6 + or - 5.6 mgNO(3)-N/gVSS/hr) are higher than that for methanol (10.1 + or - 2.5 mgNO(3)-N/gVSS/hr). The yield coefficients in g COD/g COD were observed to follow a similar trend with values of 0.45 + or - 0.05 for methanol, 0.53 + or - 0.06 for ethanol and 0.66 + or - 0.06 for acetate.

Evaluation of alternative electron donors for denitrifying moving bed biofilm reactors (MBBRs)

The effectiveness of four different electron donors, specifically methanol, ethanol, glycerol, and sulfide (added as Na(2)S), were evaluated in post-denitrifying bench-scale moving bed biofilm reactors (MBBRs). With the requirement for more wastewater treatment plants to reach effluent total nitrogen levels approaching 3 mg/L, alternative electron donors could promote more rapid MBBR startup/acclimation times and increased cold weather denitrification rates compared to methanol, which has been most commonly used for post-denitrification processes due to low cost and effectiveness. While the application of alternative substrates in suspended growth processes has been studied extensively, fixed film post denitrification processes have been designed to use primarily low yield substrates like methanol. Bench-scale MBBRs were operated continuously at 12 degrees Celsius, and performance was monitored by weekly sampling and insitu batch profile testing. Ethanol and glycerol, though visually exhibited much higher biofilm carrier biomass content, performed better than methanol in terms of removal rate (0.9 and 1.0 versus 0.6 g N/m(2)/day, respectively.) Maximum denitrification rate measurements from profile testing suggested that ethanol and glycerol (2.2 and 1.9 g N/m(2)/day, respectively) exhibited rates that were four times that of methanol (0.49 g N/m(2)/day.) Sulfide also performed much better than either of the other three electron donors with maximum rates at 3.6 g N/m(2)/day and with yield (COD/NO(3)-N) that was similar to or slightly less than that of methanol.

Uncoupling the solids retention times of flocs and granules in mainstream deammonification: A screen as effective out-selection tool for nitrite oxidizing bacteria

This study focused on a physical separator in the form of a screen to out-select nitrite oxidizing bacteria (NOB) for mainstream sewage treatment. This separation relied on the principle that the NOB prefer to grow in flocs, while anammox bacteria (AnAOB) reside in granules. Two types of screens (vacuum and vibrating) were tested for separating these fractions. The vibrating screen was preferred due to more moderate normal forces and additional tangential forces, better balancing retention efficiency of AnAOB granules (41% of the AnAOB activity) and washout of NOB (92% activity washout). This operation resulted in increased NOB out-selection (AerAOB/NOB ratio of 2.3) and a total nitrogen removal efficiency of 70% at influent COD/N ratio of 1.4. An effluent total nitrogen concentration <10mgN/L was achieved using this novel approach combining biological selection with physical separation, opening up the path towards energy positive sewage treatment.

Optimization of a mainstream nitritation-denitritation process and anammox polishing

This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process that was followed by anammox polishing. The pilot plant treated real municipal wastewater at ambient temperatures. The effluent of high-rate activated sludge process (hydraulic retention time, HRT=30 min, solids retention time=0.25 d) was fed to the pilot plant described in this paper, where a constant temperature of 23 °C was maintained. The nitritation-denitritation process was operated to promote nitrite oxidizing bacteria out-selection in an intermittently aerated reactor. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia and nitrate+nitrite concentrations. The unique feature of this aeration control was that fixed dissolved oxygen set-point was used and the length of aerobic and anoxic durations were changed based on the effluent ammonia and nitrate+nitrite concentrations. The anaerobic ammonia oxidation (anammox) bacteria were adapted in mainstream conditions by allowing the growth on the moving bed bioreactor plastic media in a fully anoxic reactor. The total inorganic nitrogen (TIN) removal performance of the entire system was 75±15% during the study at a modest influent chemical oxygen demand (COD)/NH4+-N ratio of 8.9±1.8 within the HRT range of 3.1-9.4 h. Anammox polishing contributed 11% of overall TIN removal. Therefore, this pilot-scale study demonstrates that application of the proposed nitritation-denitritation system followed by anammox polishing is capable of relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT.

Expanding DEMON Sidestream Deammonification Technology Towards Mainstream Application.

A cross-Atlantic R&D-cooperation involving three large utilities investigated the feasibility of mainstream deammonification-the application of partial nitritation/anammox for full-plant treatment of municipal wastewater at ambient temperatures. Two major process components have been implemented, 1) bioaugmentation of aerobic- and anaerobic ammonia oxidizers (AOB and AMX) from the DEMON-sidestream sludge liquor treatment to the mainstream and 2) implementation of hydrocyclones to select for anammox granules and retain them in the system. Different operation modes have been tested at laboratory- and pilot-scale in order to promote the short-cut (more direct anammox route) in nitrogen removal metabolism. At the full-scale installation at Strass WWTP, stable repression of nitrite oxidizing biomass (NOB) has been achieved for several months. Significant anammox enrichment in the mainstream has been monitored while high efficiency in the sidestream-process has been maintained (96% annual average ammonia removal).