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.     

Increases in fecal coliform bacteria resulting from centrifugal dewatering of digested biosolids

In many countries, the classification of biosolids for disposal purposes can be based, in part, on fecal coliform levels, with alternative criteria also available based on the stabilization process used, such as anaerobic digestion. The assumption that these alternative criteria provide equivalent protection may be flawed. This paper demonstrates that fecal coliform levels determined after digestion do not always indicate the bacterial levels after the same biosolids have been dewatered by centrifugation. In samples from mesophilic digestion, half had significant increases in coliform numbers (P<0.05) with up to one order of magnitude increase during centrifugation, suggesting coliform regrowth. Thermophilically digested samples had significant increases of several orders of magnitude during dewatering, more likely from reactivation of viable but non-culturable coliforms than from regrowth. In other cases, centrifugation induced coliform regrowth or reactivation upon incubation and storage of dewatered samples, but not digested samples. These 2-3 order of magnitude increases occurred with both 25 and 37 degrees C incubations. Coliform increases continued for up to 5 days, then gradually declined. However, by day 20 coliform numbers were still 2 orders of magnitude greater than when originally sampled. The magnitude of the increases could be due either to regrowth or reactivation, but the nature of the longer-term increases--also seen in biosolids/soil mixtures--suggests regrowth. Differences in numbers between digested and dewatered samples could not be duplicated with high shear processing in lab-scale devices, with nitrogen purging to remove volatile or gaseous constituents, or with redilution using centrate. They could not be attributed to enumeration methods, to interference of Bacillus spp. on apparent coliform counts, or to temperature changes. The increases have practical implications in the use of fecal coliform or alternative criteria to define pathogen content in biosolids.     

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.     

Investigation of indoor chemical pollutants and perceived odor in an area with complaints of unpleasant odors

An uncomfortable smell was reported by employees of an IT office (information technological office) in a medical center. This problem started two years ago when the office was refurbished. The objectives of this study are to characterize the indoor air quality of this complaint area in terms of chemical pollutants and odor characteristics, and identify possible sources of this foul smell. Carbonyl chemicals and volatile organic compounds (VOCs) were investigated in this study, since these two groups are associated with odors and health effects. Additionally, the odor was evaluated by odor assessors (non-smokers) who recorded odor characters that appeared in offices. By comparing chemical measurements between complaint and non-complaint areas, calculating odor indices, and correlating odor and chemical measurements, we got results showing that a higher correlation coefficient is found between odor presence frequencies and VOC concentrations. Further investigating found nonanal and decanal are possible chemicals for malodors. The concentration levels of these two chemicals in the complaint area are higher than those in the non-complaint areas and exceeding odor thresholds. Possible sources of these long-chain aldehydes are formed during the oxidation degradations of fatty acids like linoleic acid, linolenic acid and oleic acid which are ingredients for many building products like linoleum and surface coating. In order to mitigate this malodor problem, extra and effective ventilation flow rate should be provided to reduce the concentrations of odorous chemicals and the precursors for these odorous chemicals.     

An evaluation of solid phase microextraction for analysis of odorant emissions from stored biosolids cake

Odors are a common occurrence at wastewater treatment plants, biosolids processing facilities and biosolids recycling locations. Accurate, objective measurement techniques are needed to monitor emissions, to develop new waste handling procedures and to reduce the production of the volatile gases. The objective of this study was to evaluate the use of solid phase microextraction for measuring common odorants that are found in biosolids facilities. The odorants were collected and concentrated by solid phase microextraction (SPME) and then quantified by gas chromatography with detection by mass spectrometry. A 75-microm Carboxen-Polydimethylsiloxane coating was used for the analysis of trimethylamine, dimethyl sulfide, dimethyl disulfide and methyl mercaptan. Gaseous standards were generated for individual compounds and for dry and wet mixture from permeation apparatus. The differences in sensitivity between fibers, the competition between analytes and water vapor for the active sites on the fiber and the lack of production of artifacts make SPME suited for qualitative analysis and enables quick screening for the identification of compounds with adverse organoleptic characteristics.     

DNA extraction and Escherichia coli quantification of anaerobically digested biosolids using the competitive touchdown PCR method

Accurate enumeration of indicator organisms such as Escherichia coli is important for assessing the safety of water and wastewater samples. Recent research has shown that E. coli can enter a viable but non-culturable state; therefore, traditional cultivation methods could potentially underestimate the quantities of the organisms. The goals of the research were to develop and verify a DNA extraction protocol and a quantitative polymerase chained reaction (PCR) method for E. coli enumeration in digested biosolids. A solvent-based DNA extraction protocol with extensive cell lysis recovered approximately 78-84% of spiked DNA. In comparison, a commercial kit only recovered 28-42% of DNA, likely from inefficient cell lysis. The developed competitive touchdown PCR (cPCR) method for E. coli enumeration was comparable to both real-time PCR (rt-PCR) and cultivation methods with sensitivity of approximately 50,000-500,000 E. coli per gram dry solids (DS), which is suitable for Class B biosolids monitoring in the US and "conventional" biosolids in the European Union. The cPCR protocol provides a less expensive alternative than the rt-PCR as a culturing independent method for enumerating E. coli.     

Perception of Odor and Nasal Pungency from Homologous Series of Volatile Organic Compounds

We tested nasal detection thresholds for airborne chemicals in a group of anosmics (i.e., subjects lacking a functional sense of smell) and in a group of age-, gender-, and smoking-status-matched normosmics (i.e., subjects with normal olfaction). Anosmics provided odor unbiased nasal pungency (irritation) thresholds. Normosmics provided odor thresholds. Homologous series of alcohols, acetates, and ketones served as stimuli. Eye irritation thresholds were also measured for selected acetates. Most substances evoked pungency (i.e., were detected by the anosmics). All sensory thresholds decreased systematically with carbon chain length. The gap between pungency and odor grew larger with increasing carbon chain length. Pungency thresholds-but not odor thresholds-showed a uniform linear relationship of slope close to unity with saturated vapor concentration, irrespective of chemical functionality or carbon chain length. This suggests that pungency from nonreactive airborne chemicals rests heavily on a relatively unspecific physical interaction with a susceptible biophase. Of relevance to indoor environments, such an interaction opens the possibility for a high degree of sensory addition of pungency from individual components of complex mixtures resulting in noticeable irritation even when each component is at a level well below threshold value.     

Characterization of intracellular & extracellular algae organic matters (AOM) of Microcystic aeruginosa and formation of AOM-associated disinfection byproducts and odor & taste compounds

Algae organic matters (AOM), including intracellular organic matters (IOM) and extracellular organic matters (EOM), are causing numerous water quality issues, among which formation of disinfection byproducts (DBPs) and odor & taste (O&T) compounds are of particular concern. In this study, physiochemical properties of IOM and EOM of Microcystic aeruginosa under an exponential growth phase (2.01 × 10¹¹/L) were comprehensively characterized. Moreover, the yields of DBPs during AOM disinfection and O&T-causing compounds were quantified. Hydrophilic organic matters accounted for 86% and 63% of DOC in IOM and EOM, respectively. Molecular weight (MW) fractions of IOM in <1 kDa, 40-800 kDa, and >800 kDa were 27%, 42%, and 31% of DOC, respectively, while EOM primarily contained 1-100 kDa molecules. Besides, a low SUVA (0.84 L/mg m) and the specific fluorescence spectra suggested that AOM (especially IOM) was principally comprised of protein-like substances, instead of humic-like matters. The formation potentials of chloroform, chloroacetic acid, and nitrosodimethylamine were 21.46, 68.29 and 0.0096 μg/mg C for IOM, and 32.44, 54.58 and 0.0189 μg/mg C for EOM, respectively. Furthermore, the dominant O&T compound produced from EOM and IOM were 2-MIB (68.75 ng/mg C) and β-cyclocitral (367.59 ng/mg C), respectively. Of note, dimethyltrisulfide became the prevailing O & T compound following anaerobic cultivation.     

Recycled water: potential health risks from volatile organic compounds and use of 1,4-dichlorobenzene as treatment performance indicator

Characterisation of the concentrations and potential health risks of chemicals in recycled water is important if this source of water is to be safely used to supplement drinking water sources. This research was conducted to: (i) determine the concentration of volatile organic compounds (VOCs) in secondary treated effluent (STE) and, post-reverse osmosis (RO) treatment and to; (ii) assess the health risk associated with VOCs for indirect potable reuse (IPR). Samples were examined pre and post-RO in one full-scale and one pilot plant in Perth, Western Australia. Risk quotients (RQ) were estimated by expressing the maximum and median concentration as a function of the health value. Of 61 VOCs analysed over a period of three years, twenty one (21) were detected in STE, with 1,4-dichlorobenzene (94%); tetrachloroethene (88%); carbon disulfide (81%) and; chloromethane (58%) most commonly detected. Median concentrations for these compounds in STE ranged from 0.81 μg/L for 1,4-dichlorobenzene to 0.02 μg/L for carbon disulphide. After RO, twenty six (26) VOCs were detected, of which 1,4-dichlorobenzene (89%); acrylonitrile (83%) chloromethane (63%) and carbon disulfide (40%) were the more frequently detected. RQ(max) were all below health values in the STE and after RO. Median removal efficiency for RO was variable, ranging from −77% (dichlorodifluoromethane) to 91.2% (tetrachloroethene). The results indicate that despite the detection of VOCs in STE and after RO, their human health impact in IPR is negligible due to the low concentrations detected. The results indicate that 1,4-dichlorobenzene is a potential treatment chemical indicator for assessment of VOCs in IPR using RO treatment.