John T. Novak

Mechanisms of floc destruction during anaerobic and aerobic digestion and the effect on conditioning and dewatering of biosolids

Laboratory anaerobic and aerobic digestion studies were conducted using waste activated sludges from two municipal wastewater treatment plants in order to gain insight into the mechanisms of floc destruction that account for changes in sludge conditioning and dewatering properties when sludges undergo anaerobic and aerobic digestion. Batch digestion studies were conducted at 20 degrees C and the dewatering properties, solution biopolymer concentration and conditioning dose requirements measured. The data indicated that release of biopolymer from sludges occurred under both anaerobic and aerobic conditions but that the release was much greater under anaerobic conditions. In particular, the release of protein into solution was 4-5 times higher under anaerobic than under aerobic conditions. Both the dewatering rate, as characterized by the specific resistance to filtration and the amount of polymer conditioning chemicals required was found to depend directly on the amount of biopolymer (protein + polysaccharide) in solution. Little difference in dewatering properties and conditioning doses was seen between the two activated sludges from different plants. Differences in the cations released between anaerobic and aerobic digestion suggest that the digestion mechanisms differ for the two types of processes. Enzyme activity data showed that during aerobic digestion, polysaccharide degradation activity decreased to near zero and this was consistent with the accumulation of polysaccharides in aerobic digesters.

Hydrolysis of macromolecular components of primary and secondary wastewater sludge by thermal hydrolytic pretreatment.

A laboratory simulation of the thermal hydrolytic pretreatment (THP) process was performed on wastewater sludge, as well as key macromolecular components: proteins, lipids, and polysaccharides. Hydrolysis temperatures from 130 to 220 degrees C were investigated. The objectives of this study were to determine how and over which temperature range THP specifically affects sludge components, and whether hydrolysis temperature can be used to minimize the previously reported drawbacks of THP such as high total ammonia nitrogen (TAN) loads and the production of highly-colored recalcitrant organics. In addition, the applicability of THP to primary sludge (PS) was investigated. The breakdown of proteins, lipids, and polysaccharides was determined to be temperature dependent, and both waste activated sludge (WAS) and PS responded similarly to THP apart from intrinsic differences in lipid and protein content. Pure carbohydrate solutions were not largely converted to mono- or dimeric reducing sugar units at temperatures below 220 degrees C, however significant caramelization of starch and production of dextrose and maltose was observed to occur at 220 degrees C. Volatile fatty acid production during thermal hydrolysis was largely attributed to the breakdown of unsaturated lipids, and long-chain fatty acid production was not significant in terms of previous reports of methanogenic inhibition. Ammonia was produced from protein during thermal hydrolysis, however solids loading rather than thermal hydrolysis temperature appeared to be a more meaningful control for ammonia levels in downstream anaerobic digestion.

Effect of Various Sludge Digestion Conditions on Sulfonamide, Macrolide, and Tetracycline Resistance Genes and Class I Integrons

Wastewater treatment processes are of growing interest as a potential means to limit the dissemination of antibiotic resistance. This study examines the response of nine representative antibiotic resistance genes (ARGs) encoding resistance to sulfonamide (sulI, sulII), erythromycin (erm(B), erm(F)), and tetracycline (tet(O), tet(W), tet(C), tet(G), tet(X)) to various laboratory-scale sludge digestion processes. The class I integron gene (intI1) was also monitored as an indicator of horizontal gene transfer potential and multiple antibiotic resistance. Mesophilic anaerobic digestion at both 10 and 20 day solids retention times (SRTs) significantly reduced sulI, suII, tet(C), tet(G), and tet(X) with longer SRT exhibiting a greater extent of removal; however, tet(W), erm(B) and erm(F) genes increased relative to the feed. Thermophilic anaerobic digesters operating at 47 °C, 52 °C, and 59 °C performed similarly to each other and provided more effective reduction of erm(B), erm(F), tet(O), and tet(W) compared to mesophilic digestion. However, thermophilic digestion resulted in similar or poorer removal of all other ARGs and intI1. Thermal hydrolysis pretreatment drastically reduced all ARGs, but they generally rebounded during subsequent anaerobic and aerobic digestion treatments. To gain insight into potential mechanisms driving ARG behavior in the digesters, the dominant bacterial communities were compared by denaturing gradient gel electrophoresis. The overall results suggest that bacterial community composition of the sludge digestion process, as controlled by the physical operating characteristics, drives the distribution of ARGs present in the produced biosolids, more so than the influent ARG composition.

Availability of sorbed toluene in soils for biodegradation by acclimated bacteria.

Abstract Batch soil microcosms were used to evaluate the sorption and bioavailability of toluene in an organic soil containing acclimated bacteria. Most toluene sorption occurs rapidly but a small fraction ( Measurement of both sorbed and solution phase toluene concentrations indicate that acclimated bacteria quickly utilize toluene under aerobic conditions. Within 2 days total toluene was reduced below measurable levels. Desorption of most toluene from soil is rapid, thereby becoming available to acclimated bacteria in the aqueous phase. However, a small quantity of toluene desorbs very slowly and becomes available for biodegradation at a rate limited by desorption.

Evaluation of the extracellular proteins in full-scale activated sludges

The proteins present in the extracellular polymeric substances (EPS) of activated sludge flocs were investigated using three cation-associated extraction methods. The subproteomes generated from four full-scale activated sludges were subsequently fractionated by ammonium sulfate precipitation and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that each extraction method led to unique SDS-PAGE protein profiles, which provided strong evidence that the extracted proteins are uniquely associated with specific cations in activated sludge flocs. The comparison of protein profiles across sludges from different treatment plants revealed that extracts obtained using a cation-exchange resin exhibited similar protein banding patterns while sulfide- and base-extracted EPS led to more variable protein profiles. Analysis of several SDS-PAGE bands by liquid chromatography-tandem mass spectrometry of tryptic digests led to the identification of several bacterial proteins as well as sewage-derived polypeptides (human elastase IIIA and keratins). Their putative roles in activated sludges and their association with targeted cations are proposed.

The effect of cationic salt addition on the settling and dewatering properties of an industrial activated sludge

Cations have been found to influence the settling and dewatering properties of activated sludge, especially for industrial wastewaters in which very high concentrations of monovalent cations are often found. Because the cation content of wastewaters is often influenced by upstream processes, an understanding of the influence of various cations can be an important consideration in pinpointing operational problems in wastewater treatment plants. An industrial activated-sludge treatment plant was studied to determine whether variations in settling and dewatering properties of the mixed liquor and waste solids could be caused by changes in the cation content of the wastewater. Laboratory reactors received both return activated sludge and wastewater from the industrial treatment plant, and the feed was supplemented with either sodium (Na + ), potassium (K + ), or magnesium (Mg + ). It was found that when the monovalent-to-divalent (M:D) cation ratio on a milliequivalent basis was increased to greater than approximately 2:1 by either Na + or K + addition, dewatering properties became poorer and polymer conditioning requirements increased. The soluble protein content also increased as the mixed liquor M:D ratio increased, indicating release of biopolymer from the flocs. Magnesium addition at low doses caused a decrease in the dewatering rate, but at higher doses both the settling and dewatering properties of waste solids improved substantially. Conversely, when Na + and K + concentrations in the raw wastewater decreased significantly to less than 10 and 0.1 milliequivalents (meq), respectively, settling and dewatering properties improved substantially and addition of Mg 2+ did not improve conditions beyond those of the unamended control. Each of the cations studied caused unique changes in the properties of activated-sludge solids that could not be correlated with the M:D ratio, suggesting that some of the effects are not simply physical/chemical but may be physiological as well.

Dewatering of Sewage Sludge

Dewatering of sewage sludges is usually carried out using belt filter presses or centrifuges. The ability to remove water from sludges by mechanical dewatering is a property of both the sludge and the equipment used for dewatering. Newer high-solids centrifuges can remove more water than a belt press but require a higher chemical conditioning dose. The Gt value, the product of the mean velocity gradient and the shear time, has been found to be a useful parameter for characterizing the shear in mechanical dewatering equipment. Dewatering can be considered a two-step process, filtration followed by expression. The expression step is the most important of these and the benefits of various sludge processing techniques and conditioning chemical types remains a fruitful area of research.

Inorganic carbon limited growth kinetics of some freshwater algae

Abstract The inorganic carbon limited growth kinetics were determined for three green and three blue-green algae over a range of light and temperatures. Anabaena flos aquae was found to be the only algae to grow at 39°C. Selenastrum capricornutum and Scenedesmus quadricauda were favored at low temperatures with Selenastrum growing best at high light and carbon levels while Scenedesmus was the most rapidly growing algae under low light, carbon and temperature conditions. Chorella was the fastest growing alga at temperatures from 27 to 33°C under all light and inorganic carbon concentrations. Neither Oscillatoria nor Microcoleus were found to be the dominant algae under the conditions tested. However, under reduced light and temperature conditions, Oscillatoria grew well at high inorganic carbon concentrations.

Effect of wastewater colloids on membrane removal of antibiotic resistance genes.

Recent studies have demonstrated that wastewater treatment plants (WWTPs) significantly alter the magnitude and distribution of antibiotic resistance genes (ARGs) in receiving environments, indicating that wastewater treatment represents an important node for limiting ARG dissemination. This study examined the potential for membrane treatment of microconstituent ARGs and the effect of native wastewater colloids on the extent of their removal. Plasmids containing vanA (vancomycin) and bla(TEM) (β-lactam) ARGs were spiked into three representative WWTP effluents versus a control buffer and tracked by quantitative polymerase chain reaction through a cascade of microfiltration and ultrafiltration steps ranging from 0.45 μm to 1 kDa. Significant removal of ARGs was achieved by membranes of 100 kDa and smaller, and presence of wastewater colloids resulted in enhanced removal by 10 kDa and 1 kDa membranes. ARG removal was observed to correlate significantly with the corresponding protein, polysaccharide, and total organic carbon colloidal fractions. Alumina membranes removed ARGs to a greater extent than polyvinylidene fluoride membranes of the same pore size (0.1 μm), but only in the presence of wastewater material. Control studies confirmed that membrane treatment was the primary mechanism of ARG removal, versus other potential sources of loss. This study suggests that advanced membrane treatment technology is promising for managing public health risks of ARGs in wastewater effluents and that removal may even be enhanced by colloids in real-world wastewaters.

Resource recovery from landfill leachate using bioelectrochemical systems: Opportunities, challenges, and perspectives

Landfill leachate has recently been investigated as a substrate for bioelectrochemical systems (BES) for electricity generation. While BES treatment of leachate is effective, the unique feature of bioelectricity generation in BES creates opportunities for resource recovery from leachate. The organic compounds in leachate can be directly converted to electrical energy through microbial interaction with solid electron acceptors/donors. Nutrient such as ammonia can be recovered via ammonium migration driven by electricity generation and ammonium conversion to ammonia in a high-pH condition that is a result of cathode reduction reaction. Metals in leachate may also be recovered, but the recovery is affected by their concentrations and values. Through integrating membrane process, especially forward osmosis, BES can recover high-quality water from leachate for applications in landscaping, agricultural irrigation or direct discharge. This review paper discusses the opportunities, challenges, and perspectives of resource recovery from landfill leachate by using BES.