Effect of total solids on fecal coliform regrowth in anaerobically digested biosolids

Fecal coliform (FC) concentrations in anaerobically digested biosolids can increase during centrifugal dewatering and afterwards in storage of dewatered cake. The immediate increase after centrifugation (reactivation) has been demonstrated to be the revitalization of fecal coliforms that had become non-culturable. The increase during storage (regrowth) has been regarded as a subsequence of reactivated bacteria growing in a favorable environment. In this paper, however, regrowth is demonstrated without preceding reactivation, using intensive laboratory centrifugation to duplicate the levels of regrowth seen in full-scale centrifugation. Higher total solids (TS) levels of the dewatered biosolids lead to greater magnitudes of FC increase. The final TS level appears much more important than the level of shear imposed during centrifugation, based on comparison of different centrifugation/dilution procedures used to obtain similar TS levels. The greater TS levels also reduce methane production, suggesting that methanogens compete with, or inhibit, the fecal coliforms. The addition of bromoethanesulfonate as a methanogen-specific inhibitor decreased the production of methane gas, and also increased the number of fecal coliforms.     

Anaerobically digested biosolids odor generation and pathogen indicator regrowth after dewatering

The objective of this research was to investigate whether a preferential stimulation of microorganisms in anaerobically digested biosolids can occur after dewatering and if it can lead to pathogen indicator regrowth and odor generation upon storage. Laboratory incubation simulating biosolids storage indicates that both odorant generation, based on total volatile organic sulfur compound concentrations (TVOSCs) and pathogen indicator regrowth, based on fecal coliform densities follow similar formation and reduction patterns. The formation and reduction patterns of both odor compounds and fecal coliforms imply that groups of microorganism are induced if shearing disturbance is imposed during dewatering, but a secondary stabilization can be achieved soon after 1-2 weeks of storage. The occurrence of the induction is likely the microbial response to substrate release and environmental changes, such as oxygen, resulting from centrifuge shearing. The new conditions favor the growth of fecal coliforms and odor producing bacteria, and therefore, results in the observed fecal coliforms regrowth and odor accumulation during subsequent storage. However, when both substrate and oxygen deplete, a secondary stabilization can be achieved, and both odor and fecal coliforms density will drop.     

Phosphorus Release and Fertiliser Value of Enhanced-Treated and Nutrient-Removal Biosolids

This paper describes a soil-incubation study which was carried out to examine the effects of (a) phosphorus removal during the treatment of domestic sewage and (b) treating sewage sludge to an enhanced status, on the phosphorus fertiliser value of biosolids which are used in agriculture. Phosphorus-enriched and conventional dewatered digested biosolids, thermally-dried pellets and granules, and digested and thermally-hydrolysed liquid sludges were incorporated into two soil types with contrasting physico-chemical properties. Plant-available phosphorus in soil was assessed after incubation by a standard chemical-extraction procedure. Sludge from biological-P removal had the highest phosphorus extract-ability in soil whereas iron dosing slightly reduced or had no effect on phosphorus release from conventionally-treated biosolids, depending upon the type of soil. High-temperature drying significantly reduced the extractable-P content in sludge by 20–60%, compared with dewatered digested cake, and release from thermally-dried biosolids declined further with iron enrichment. Extractable-P recovery was greater from all types of biosolids when mixed with calcareous soil, compared with a loamy sand. A preliminary investigation of phosphorus mineralogy in biosolids, using advanced analytical techniques, is also described.     

Mechanisms of microwave irradiation involved in the destruction of fecal coliforms from biosolids

Microwaves have been found to be effective in destructing pathogens in sewage sludge (biosolids) (75th Annual Water Environment Federation Conference, Chicago, September 29-October 2, 2002; Third World Water Congress, International Water Association, Melbourne, Australia, April 7-12, 2002). Mechanisms and roles of microwaves on fecal coliform destruction were investigated using bacterial viability tests, electron transport system (ETS) and beta-galactosidase activity assays, gel electrophoresis, and genomic deoxyribonucleic acid (DNA) optical density (OD) measurements with fecal coliforms isolated from biosolids. Bacterial viability tests demonstrated cell membrane damage as microwave irradiation intensity and temperature increased. Above 60+/-3 degrees C, viable cells were rarely found when pure fecal coliforms were irradiated with microwaves. ETS and beta-galactosidase activity assays revealed increased activity for externally heated samples due to fecal coliform growth but decreased activity for microwave-irradiated samples as temperature was increased from 20 degrees C to 57 degrees C, indicating other destruction mechanisms besides heating. Between 57 degrees C and 68 degrees C, microwave irradiation led to a more rapid decrease in activity than external heating by convection. Above 68 degrees C, bacterial activity almost ceased for both pretreatments. DNA bands in gel electrophoresis tests and OD of genomic DNA decreased more rapidly for microwave-irradiated samples than for externally heated samples, implying that microwaves disrupted DNA in fecal coliform cells at lower temperatures than external heating. Microwave irradiation of sludge appears to be a viable and economical method of destructing pathogens and generating environmentally safe sludge.     

Hydrolysis of 4-methylumbelliferyl-beta-D-glucuronide in differing sample fractions of river waters and its implication for the detection of fecal pollution

The hydrolysis rate of 4-methylumbelliferyl-beta-D-glucuronide (MUG-HR) was determined in unamended samples, filtered samples, and in corresponding buffer resuspended filter residues of various river waters of slight to excessive fecal pollution covering a four orders of magnitude range. Regression analysis of the log MUG-HR of the unamended water samples versus the log MUG-HR of the filter residues revealed a highly significant linear relationship (R2 = 0.94; p<0.001). The median of the MUG-HR of the filtrated water samples was about 10% the MUG-HR of the corresponding unamended water samples. If MUG-HR determinations were used as a surrogate for estimating fecal coliform contamination, both the MUG-HR of the unamended water samples and the MUG-HR of the filter residues would have been equally adequate techniques at river sites of higher fecal pollution levels. However, at river locations of decreased fecal pollution, MUG-HR determination of filter residues appeared to be the more sensitive technique in order to estimate fecal coliform concentrations.     

The effect of thermal hydrolysis pretreatment on the anaerobic degradation of nonylphenol and short-chain nonylphenol ethoxylates in digested biosolids

The presence of micropollutants can be a concern for land application of biosolids. Of particular interest are nonylphenol diethoxylate (NP₂EO), nonylphenol monoethoxylate (NP₁EO), and nonylphenol (NP), collectively referred to as NPE, which accumulate in anaerobically digested biosolids and are subject to regulation based on the environmental risks associated with them. Because biosolids are a valuable nutrient resource, it is essential that we understand how various treatment processes impact the fate of NPE in biosolids. Thermal hydrolysis (TH) coupled with mesophilic anaerobic digestion (MAD) is an advanced digestion process that destroys pathogens in biosolids and increases methane yields and volatile solids destruction. We investigated the impact of thermal hydrolysis pretreatment on the subsequent biodegradation of NPE in digested biosolids. Biosolids were treated with TH, anaerobic digestion, and aerobic digestion in laboratory-scale reactors, and NPE were analyzed in the influent and effluent of the digesters. NP₂EO and NP₁EO have been observed to degrade to the more estrogenic NP under anaerobic conditions; therefore, changes in the ratio of NP:NPE were of interest. The increase in NP:NPE following MAD was 56%; the average increase of this ratio in four sets of TH-MAD samples, however, was only 24.6 ± 3.1%. In addition, TH experiments performed in pure water verified that, during TH, the high temperature and pressure alone did not directly destroy NPE; TH experiments with NP added to sludge also showed that NP was not destroyed by the high temperature and pressure of TH when in a more complex sludge matrix. The post-aerobic digestion phases removed NPE, regardless of whether TH pretreatment occurred. This research indicates that changes in biosolids processing can have impacts beyond just gas production and solids destruction.     

Nitrogen Release and Fertiliser Value of Thermally-Dried Biosolids

Nitrogen production from five thermally-dried biosolids plants was measured in two contrasting soil types and compared with samples of undried digested sludge cake from the same treatment works, using a controlled laboratory incubation-extraction procedure. Inorganic-N was lost from the digested biosolids during high-temperature drying by ammonia volatilisation. Nevertheless, the production of nitrate-N in soil amended with thermally-dried biosolids was similar to, or greater than, conventionally-treated dewatered sludge. The results indicate that thermal conditioning significantly increases the mineralisable organic-N content in digested biosolids. Soil properties had subtle effects on the patterns of nitrogen release, but did not significantly affect the overall accumulation of mineral-N from the biosolids. The results showed that thermally-dried anaerobically-digested biosolids are potentially highly-consistent products and effective replacements for inorganic-N fertiliser in agricultural production.     

The ecology of "fecal indicator" bacteria commonly found in pulp and paper mill water systems

Coliform bacteria have long been used to indicate fecal contamination of water and thus a health hazard. In this study, the in-mill water and external effluent treatment systems of seven typical Canadian pulp and paper mills were all shown to support the growth of numerous coliforms, especially Klebsiella Spp., Escherichia coli. Enterobacter spp., and Citrobacter spp. In all mills and most sampled locations, klebsiellas were the predominant coliforms. Although all but one of the mills had no sewage input and most disinfected their feed (input) water, all contained the most typical fecal indicator bacterium, E. coli. Many of the mill coliforms were classified as fecal coliforms by standard "MPN" and metabolic tests, but this was shown to be due to their thermotolerance, not their origin. Mill coliforms were shown not to be just simple transients from feedwater or furnish (wood), but to be continuously growing, especially in some of the primary clarifiers. Isolated mill coliforms grew very well on a sterilized raw combined mill effluent. The fecal streptococci (enterococci), alternative indicators of fecal health hazards, were common in all mills in the absence of sewage. Ten strains of E. coli isolated from four mills were all shown to be non-toxigenic strains of harmless serotypes. No salmonellas were found. Therefore, the use of total coliform, fecal coliform, enterococci, or E. coli counts as indicators of fecal contamination, and thus of health hazard in pulp and paper mill effluents or biosolids (sludges) known to be free of fecal input is invalid.     

Reactivation and growth of non-culturable indicator bacteria in anaerobically digested biosolids after centrifuge dewatering

Recent literature has reported that high concentrations of indicator bacteria such as fecal coliforms (FCs) were measured in anaerobically digested sludges immediately after dewatering even though low concentrations were measured prior to dewatering. This research hypothesized that the indicator bacteria can enter a non-culturable state during digestion, and are reactivated during centrifuge dewatering. Reactivation is defined as restoration of culturability. To examine this hypothesis, a quantitative polymerase chain reaction (qPCR) method was developed to enumerate Escherichia coli, a member of the FC group, during different phases of digestion and dewatering. For thermophilic digestion, the density of E. coli measured by qPCR could be five orders of magnitude greater than the density measured by standard culturing methods (SCMs), which is indicative of non-culturable bacteria. For mesophilic digestion, qPCR enumerated up to about one order of magnitude more E. coli than the SCMs. After centrifuge dewatering, the non-culturable organisms could be reactivated such that they are enumerated by SCMs, and the conditions in the cake allowed rapid growth of FCs and E. coli during cake storage.     

Effects of sludge dewatering and digestion processes on Escherichia coli enumeration

Centrifuge dewatering digested sewage sludge has been reported to significantly increase numbers of Escherichia coli, potentially exceeding the UK microbiological standards of 10³ or 10⁵ E. coli/g dry solids (DS) for enhanced or conventional treatment for agricultural use, respectively. Here, we report an investigation of the effects of different types of dewatering process on E. coli enumeration in conventionally treated, anaerobically digested sludge (primary and secondary liquid digestion), as well as raw sludge at eight wastewater treatment works in the United Kingdom. The dewatering methods evaluated included: centrifuge conditioning and filter-belt and filter-plate pressing. The results demonstrated that conventional treatment by primary and secondary liquid digestion and dewatering conditioning produces biosolids compliant with UK maximum microbiological limits for agricultural application.     

Fecal coliform accumulation within a river subject to seasonally-disinfected wastewater discharges

As pathogen contamination is a leading cause of surface water impairment, there has been increasing interest in the implications of seasonal disinfection practices of wastewater effluents for meeting water quality goals. For receiving waters designated for recreational use, disinfection during the winter months is often considered unnecessary due to reduced recreational usage, and assumptions that lower temperatures may reduce pathogen accumulation. For a river subject to seasonal disinfection, we sought to evaluate whether fecal coliforms accumulate during the winter to concentrations that would impair river water quality. Samples were collected from municipal wastewater outfalls along the river, as well as upstream and downstream of each outfall during the winter, when disinfection is not practiced, and during the summer, when disinfection is practiced. During both seasons, fecal coliform concentrations reached 2000–5000 CFU/100 mL, nearly an order of magnitude higher than levels targeted for the river to achieve primary contact recreational uses. During the summer, wastewater effluents were not significant contributors to fecal coliform loadings to the river. During the winter, fecal coliform accumulated along the river predominantly due to loadings from successive wastewater outfalls. In addition to the exceedance of fecal coliform criteria within the river, the accumulation of wastewater-derived fecal coliform along the river during the winter season suggests that wastewater outfalls may contribute elevated loads of pathogens to the commercial shellfish operations occurring at the mouth of the river. Reductions in fecal coliform concentrations between wastewater outfalls were attributed to dilution or overall removal. Combining discharge measurements from gauging stations, tributaries and wastewater outfalls to estimate seepage, dilution between wastewater outfalls was estimated, along with the percentage of the river deriving from wastewater outfalls. After accounting for dilution, the residual reductions in fecal coliform concentrations observed between outfalls were attributed to actual fecal coliform removal. The estimated rate of removal of 1.52 d^?1 was significantly higher than die-off rates determined by previous researchers at similarly low temperatures in laboratory batch experiments, indicating the potential importance of other removal mechanisms, such as predation or sedimentation.     

Sediment bags as an integrator of fecal contamination in aquatic systems

The identification of sources of fecal pollution in urban streams or storm sewers is often difficult since fecal contamination events frequently are episodic and/or have ceased before a survey can be undertaken. As an alternative to sampling the water column and/or natural sediments, sediment bags suspended in the water column can act to integrate water quality data with respect to fecal coliform concentrations. Furthermore, sediment bags retain coliform bacteria after their initial sorption to the sand substrate. As a result, they can identify contaminant sources even though, as is often the case, the sampling survey is carried out after the pollution event.     

Some effects of shoreline cottage development on lake bacteriological water quality

Eighteen cottaged lakes and one uncottaged lake in Southern Ontario, and their inflowing streams were surveyed for bacterial indicators of pollution by membrane filter techniques. Water samples were taken on 5 consecutive days in the spring, summer, and fall of the year. Inputs of fecal indicator bacteria were determined through an analysis of variance. Fecal coliform and fecal streptococcus levels in lakewater varied in a seemingly erratic manner. When the bacterial densities at different points on the lake were examined by an analysis of variance, the locations with significantly higher densities of fecal coliforms and fecal streptococci were most often found along the cottaged shoreline. Total coliform densities did not show this relationship with the cottaged shoreline. In addition, after rainfall, a large increase in numbers of fecal coliforms were found in the cottaged lakes but not in the uncottaged lake. These findings indicated that the cottaged shoreline was a greater source of fecal indicator bacteria than the uncottaged shoreline. However, the highest concentrations of fecal indicator bacteria in these lakes were found in the inflowing streams. The bacteria in these streams arose from stormwater from undeveloped forested watersheds and were probably, therefore, of soil or animal origin.     

Sequential modeling of fecal coliform removals in a full-scale activated-sludge wastewater treatment plant using an evolutionary process model induction system

We propose an evolutionary process model induction system that is based on the grammar-based genetic programming to automatically discover multivariate dynamic inference models that are able to predict fecal coliform bacteria removals using common process variables instead of directly measuring fecal coliform bacteria concentration in a full-scale municipal activated-sludge wastewater treatment plant. A sequential modeling paradigm is also proposed to derive multivariate dynamic models of fecal coliform removals in the evolutionary process model induction system. It is composed of two parts, the process estimator and the process predictor. The process estimator acts as an intelligent software sensor to achieve a good estimation of fecal coliform bacteria concentration in the influent. Then the process predictor yields sequential prediction of the effluent fecal coliform bacteria concentration based on the estimated fecal coliform bacteria concentration in the influent from the process estimator with other process variables. The results show that the evolutionary process model induction system with a sequential modeling paradigm has successfully evolved multivariate dynamic models of fecal coliform removals in the form of explicit mathematical formulas with high levels of accuracy and good generalization. The evolutionary process model induction system with sequential modeling paradigm proposed here provides a good alternative to develop cost-effective dynamic process models for a full-scale wastewater treatment plant and is readily applicable to a variety of other complex treatment processes.     

Pilot-scale evaluation of ozone and biological activated carbon for trace organic contaminant mitigation and disinfection

In an effort to validate the use of ozone for contaminant oxidation and disinfection in water reclamation, extensive pilot testing was performed with ozone/H₂O₂ and biological activated carbon (BAC) at the Reno-Stead Water Reclamation Facility in Reno, Nevada. Three sets of samples were collected over a five-month period of continuous operation, and these samples were analyzed for a suite of trace organic contaminants (TOrCs), total estrogenicity, and several microbial surrogates, including the bacteriophage MS2, total and fecal coliforms, and Bacillus spores. Based on the high degree of microbial inactivation and contaminant destruction, this treatment train appears to be a viable alternative to the standard indirect potable reuse (IPR) configuration (i.e., membrane filtration, reverse osmosis, UV/H₂O₂, and aquifer injection), particularly for inland applications where brine disposal is an issue. Several issues, including regrowth of coliform bacteria in the BAC process, must be addressed prior to full-scale implementation.     

Particle-associated microorganisms in stormwater runoff

This research investigated the effects of blending and chemical addition before analysis of the concentration of microorganisms in stormwater runoff from a single summer storm to determine whether clumped or particle-associated organisms play a significant role. The standard membrane filtration method was used to enumerate the microorganisms. All organisms, except for Escherichia coli, showed an increase in the measured concentration after blending samples at 22,000 rpm with or without the chemical mixture. Other than fecal streptococci, the organism concentrations decreased with the addition of the Camper's solution in both blended and unblended samples before analyses. There was a statistically significant interaction between the effects of Camper's solution and the effects of blending for all the organisms tested, except for total coliform. Blending did not alter the mean particle size significantly. The results show no correlation between increased total coliform, fecal coliform, and fecal streptococcus concentrations and the mean particle size.     

Distribution of indicator bacteria in Canyon Lake, California

The spatial and temporal distributions of indicator bacteria in a small, multiple-use source drinking water reservoir in Southern California, USA were quantified over the period August 2001-July 2002. High levels of total and fecal coliform bacteria were present in Canyon Lake (annual geometric mean concentrations+/-SEM of 3.93+/-0.02 and 3.02+/-0.03 log cfu/100mL, respectively), while comparatively low levels of enterococci and E. coli were found (1.16+/-0.02 log cfu/100mL and 0.30+/-0.03 log MPN/100mL, respectively). As a result, these different indicator bacteria yielded quite divergent indices of water quality, with 72.1% of all surface samples (n=294) exceeding the USEPA single-sample limit of 400 cfu/100mL fecal coliform bacteria, while none (0%) of the samples exceeded the single-sample limit for E. coli (n=194). Regression analyses found a positive correlation between total and fecal coliform bacteria (R=0.50, significant at p<0.001) and between enterococci and E. coli (R=0.51, significant at p<0.001), but no correlation or inverse correlations were found between coliform concentrations and enterococci and E. coli levels. External sources responsible for the high total and fecal coliform bacteria were not identified, although laboratory studies demonstrated growth of the coliform bacteria in lake water samples. Enterococci and E. coli were not observed to grow, however. Bacteria concentrations varied relatively little laterally across the lake, although strong vertical gradients in fecal coliform and enterococcus bacteria concentrations were present during summer stratification, with concentrations about 10x higher above the thermocline when compared with surface concentrations. In contrast, total bacteria, total virus and total coliform bacteria levels were unchanged with depth. Seasonal trends in bacteria concentrations were also present. This study shows that the choice of indicator bacteria and sampling depth can both strongly affect the apparent microbial water quality of a lake or reservoir.     

Economics of Recovering Value from Recycling Treated Biosolids to Land

This paper demonstrates the economic value of recycling treated biosolids to land in terms of (a) the effect on agricultural yield and (b) the avoidance of environmental and social costs of using conventional mineral fertilisers. Replicated field trials show that yield increases can be achieved when biosolids are used in conjunction with mineral fertilisers, compared with using conventional fertilisers. Relevant environmental and social costs of the production and use of both nitrogen and phosphate fertilisers and recycled biosolids are estimated. By recycling biosolids to agricultural land, the external costs associated with conventional mineral fertilisers can be fully recovered. The total replacement value of biosolids is the sum of the values of the increased yields and the replaced external costs. For digested cake this is equal to £2.64/tonne and for granules £10.85/tonne; in both cases the replacement value exceeds the external costs of biosolids. These costs and benefits should be taken into account in the development of environmental policy related to wastewater treatment.     

Study on chlorine disinfection of pond effluent

Chlorine disinfection experiments were conducted to investigate the die-off patterns of the fecal coliforms when present in waste stabilization pond effluents containing from 100 to 400 mg l⁻¹ algae. The fecal coliform inactivation was observed to occur at two rates, i.e. an initial rapid kill followed by a slower kill. The magnitude of inactivation was found to be proportional to the initial chlorine dose and contact time and inversely proportional to the algal concentration. A mathematical model was developed to predict the fecal coliform survival ratio during the chlorination of the pond effluent. When compared with the experimental data, the predicted results had a correlation coefficient of 0.981.