Ulas Tezel

Methane recovery from the anaerobic codigestion of municipal sludge and FOG

The anaerobic biodegradability of a mix of municipal primary sludge (PS), thickened waste activated sludge (TWAS) and fat, oil, and grease (FOG) was assessed using semi-continuous feed, laboratory-scale anaerobic digesters operated at mesophilic (35 degrees C) and thermophilic (52 degrees C) temperature. Addition of a large FOG fraction (48% of the total VS load) to a PS+TWAS mix, resulted in 2.95 times larger methane yield, 152 vs. 449 mL methane @ STP/g VS added at 35 degrees C and 2.6 times larger methane yield, 197 vs. 512 mL methane @ STP/g VS added at 52 degrees C. The high FOG organic load fraction was not inhibitory to the process. The results of this study demonstrate the benefit of sludge and FOG codigestion.

Quaternary ammonium disinfectants: microbial adaptation, degradation and ecology

Disinfectants play an important role in maintaining acceptable health standards by significantly reducing microbial loads as well as reducing, if not eliminating, pathogens. This review focuses on quaternary ammonium compounds (QACs), a widely used class of organic disinfectants. Specifically, it reviews the occurrence, microbial adaptation, and degradation of QACs, focusing on recent reports on the ecology of QAC-degraders, the pathways and mechanisms of microbial adaptation which lead to resistance to QACs, as well as to antibiotics. With the help of culture-dependent and nonculture-dependent tools, as well as advanced analytical techniques, a better understanding of the fate and effect of QACs and their biotransformation products is emerging. Understanding the underlying mechanisms and conditions that result in QAC resistance and biodegradation will be instrumental in the prudent use of existing QAC formulations and foster the development of safer disinfectants. Development and implementation of (bio)technologies for the elimination of QACs from treated wastewater effluents will lessen adverse impacts to both humans and the environment.

Long-Term Exposure to Benzalkonium Chloride Disinfectants Results in Change of Microbial Community Structure and Increased Antimicrobial Resistance

The effect of benzalkonium chlorides (BACs), a widely used class of quaternary ammonium disinfectants, on microbial community structure and antimicrobial resistance was investigated using three aerobic microbial communities: BACs-unexposed (DP, fed a mixture of dextrin/peptone), BACs-exposed (DPB, fed a mixture of dextrin/peptone and BACs), and BACs-enriched (B, fed only BACs). Long-term exposure to BACs reduced community diversity and resulted in the enrichment of BAC-resistant species, predominantly Pseudomonas species. Exposure of the two microbial communities to BACs significantly decreased their susceptibility to BACs as well as three clinically relevant antibiotics (penicillin G, tetracycline, ciprofloxacin). Increased resistance to BACs and penicillin G of the two BACs-exposed communities is predominantly attributed to degradation or transformation of these compounds, whereas resistance to tetracycline and ciprofloxacin is largely due to the activity of efflux pumps. Quantification of several key multidrug resistance genes showed a much higher number of copies of these genes in the DPB and B microbial communities compared to the DP community. Collectively, our findings indicate that exposure of a microbial community to BACs results in increased antibiotic resistance, which has important implications for both human and environmental health.

Sorption of quaternary ammonium compounds to municipal sludge

The sorptive behavior of four quaternary ammonium compounds (QACs) - hexadecyl trimethyl ammonium chloride (C(16)TMA), dodecyl trimethyl ammonium chloride (C(12)TMA), hexadecyl benzyl dimethyl ammonium chloride (C(16)BDMA), and dodecyl benzyl dimethyl ammonium chloride (C(12)BDMA) - to municipal primary, waste activated, mesophilic digested, and thermophilic digested sludges was assessed at 22 degrees C. Batch adsorption of all four separately tested QACs to primary sludge reached equilibrium within 4h. At a nominal, initial QAC concentration of 300mg/L and a sludge volatile solids concentration of 1g/L, the extent of adsorption was 13, 88, 67, and 89% for the C(12)TMA, C(16)TMA, C(12)BDMA, and C(16)BDMA, respectively, and correlated positively to the QAC hydrophobicity and negatively to their critical micelle concentration. Equilibrium partitioning data were described by the Freundlich isotherm model. The adsorption capacity of the four sludges was very similar. In binary QAC mixtures, QACs with relatively high adsorption affinity and at relatively high aqueous concentrations decreased the adsorption of QACs with a low adsorption affinity. At pH 7, about 40% of the sludge-C(12)TMA desorbed, whereas less than 5% of the sludge-C(16)BDMA desorbed in 10 days. The effect of pH was negligible on the desorption extent of C(12)TMA at a pH range 4-10 over 10 days, whereas increasing the solution pH to 10 resulted in more than 50% desorption of C(16)BDMA. Given the fact that approximately 50% of the municipal biosolids are land-applied in the US, the data of this study would help in the assessment of the fate of QACs and their potential effect on human and environmental health.

Evaluation and modeling of benzalkonium chloride inhibition and biodegradation in activated sludge

The inhibitory effect and biodegradation of benzalkonium chloride (BAC), a mixture of alkyl benzyl dimethyl ammonium chlorides with different alkyl chain lengths, was investigated at a concentration range from 5 to 20 mg/L and different biomass concentrations in an activated sludge system. A solution containing glucose and mineral salts was used as the wastewater in all the assays performed. The inhibition of respiratory enzymes was identified as the mode of action of BAC as a result of oxygen uptake rate analysis performed at BAC concentrations ranging between 5 and 70 mg/L. The glucose degradation in the activated sludge at different BAC and biomass concentrations was well-described with Monod kinetics with competitive inhibition. The half-saturation inhibition constant (K(I)) which is equivalent to EC(50) of BAC for the activated sludge tested ranged between 0.12 and 3.60 mg/L. The high K(I) values were recorded at low BAC-to-biomass ratios, i.e. less than 10 mg BAC/g VSS, at which BAC was almost totally adsorbed to biomass and not bioavailable. BAC degradation started as soon as glucose was totally consumed. Although BAC was almost totally adsorbed on the biomass, it was degraded completely. Therefore, BAC degradation was modeled using two-phase biodegradation kinetics developed in this study. This model involves rapid partitioning of BAC to biomass and consecutive degradation in both aqueous and solid phases. The aqueous phase BAC degradation rate was twenty times, on average, higher than the solid phase degradation rate. The specific aqueous (k(I1)) and solid (k(I2)) phase BAC utilization rate constants were 1.25 and 0.31 mg BAC/g VSS h, respectively. The findings of this study would help to understand the reason of extensive distribution of quaternary ammonium compounds in wastewater treatment plant effluents and in natural water systems although QACs are biodegradable, and develop strategies to avoid their release and accumulation in the environment.

Fate and effect of naphthenic acids on oil refinery activated sludge wastewater treatment systems

Naphthenic acids (NAs) are a complex group of alkyl-substituted acyclic, monocyclic and polycyclic carboxylic acids present in oil sands process waters, crude oil, refinery wastewater and petroleum products. Crude oil, desalter brine, influent, activated sludge mixed liquor and effluent refinery samples were received from six United States refineries. The total acid number (TAN) of the six crudes tested ranged from 0.12 to 1.5 mg KOH/g crude oil and correlated to the total NA concentration in the crudes. The total NA concentration in the desalter brine, influent, activated sludge mixed liquor and effluent samples ranged from 4.2 to 40.4, 4.5 to 16.6, 9.6 to 140.3 and 2.8 to 11.6 mg NA/L, respectively. The NAs in all wastewater streams accounted for less than 16% of the total COD, indicating that many other organic compounds are present and that NAs are a minor component in refinery wastewaters. Susceptibility tests showed that none of the activated sludge heterotrophic microcosms was completely inhibited by NAs up to 400 mg/L. Growth inhibition ranging from 10 to 59% was observed in all microcosms at and above 100 mg NA/L. NAs chronically-sorbed to activated sludge mixed liquor biomass and powdered activated carbon (PAC) were recalcitrant and persistent. More than 80% of the total NAs remained in the solid phase at the end of the 10-day desorption period (five successive desorption steps). Throughout a 90-day incubation period, the total NA concentration decreased by 33 and 51% in PAC-free and PAC-containing mixed liquor microcosms, respectively. The lower molecular weight fraction of NAs was preferentially degraded in both mixed liquors. The persistence of the residual, higher molecular weight NAs is likely a combination of molecular recalcitrance and decreased bioavailability when chronically-sorbed to the biomass and/or PAC.

Mesophilic and thermophilic anaerobic digestion of municipal sludge and fat, oil, and grease.

The anaerobic biodegradability of municipal primary sludge, thickened waste activated sludge (TWAS), and fat, oil, and grease (FOG) was assessed using semi-continuous-feed, laboratory-scale anaerobic digesters and compared with the ultimate degradability obtained from 120-day batch digestion at 35 degrees C. In run 1, combined primary sludge and TWAS (40/60%, volatile solids [VS] basis) were fed to digesters operated at mesophilic (35 degrees C) and thermophilic (52 degrees C) temperatures at loading rates of 0.99 and 1.46 g-VS/L x d for primary sludge and TWAS, respectively, and a hydraulic retention time (HRT) of 12 days. The volatile solids destruction values were 25.3 and 30.7% (69 and 83% biodegradable volatile solids destruction) at 35 degrees C and 52 degrees C, respectively. The methane (CH4) yields were 159 and 197 mL at the standard temperature and pressure (STP) conditions of 0 degree C and 1 atm/g-VS added or 632 and 642 mL @ STP/g-VS destroyed at 35 degrees C and 52 degrees C, respectively. In run 2, a mix of primary sludge, TWAS, and FOG (21/31/48%, volatile solids basis) was fed to an acid digester operated at a 1-day HRT, at 35 degrees C, and a loading rate of 52.5 g-VS/L x d. The acid-reactor effluent was fed to two parallel methane-phase reactors operated at an HRT of 12 days and maintained at 35 degrees C and 52 degrees C, respectively. After an initial period of 20 days with near-zero gas production in the acid reactor, biogas production increased and stabilized to approximately 2 mL CH4 @ STP/g-VS added, corresponding to a volatile solids destruction of 0.4%. The acid-phase reactor achieved a 43% decrease in nonsaturated fat and a 16, 26, and 20% increase of soluble COD, volatile fatty acids, and ammonia, respectively. The methane-phase volatile solids destruction values in run 2 were 45 and 51% (85 and 97% biodegradable volatile solids destruction) at 35 degrees C and 52 degrees C, respectively. The methane yields for the methane-phase reactors were 473 and 551 mL @ STP/g-VS added, which is approximately 3 times larger compared with run 1, or 1040 and 1083 mL @ STP/g-VS destroyed, at 35 degrees C and 52 degrees C, respectively. The results indicate that, when co-digesting municipal sludge and FOG, a large FOG organic load fraction could have a profound effect on the methane gas yield.

Aerobic biotransformation of n-tetradecylbenzyldimethylammonium chloride by an enriched Pseudomonas spp. community.

The biotransformation of n-tetradecylbenzyldimethylammonium chloride (C(14)BDMA-Cl), a quaternary ammonium compound (QAC), under aerobic conditions by an enriched microbial community growing on benzalkonium chlorides (BACs) was investigated. Biotransformation of C(14)BDMA-Cl commenced with cleavage of the C(alkyl)-N bond and formation of benzyldimethylamine (BDMA). BDMA was further degraded, but in contrast to a previously reported BAC biotransformation pathway, neither benzylmethylamine (BMA) nor benzylamine (BA) was detected as a BDMA biotransformation product. Kinetic assays further confirmed that BMA and BA were not intermediates of C(14)BDMA-Cl transformation by the enriched community. Thus, BDMA is thought to be transformed to dimethylamine and benzoic acid via debenzylation. The biomass-normalized rate of C(14)BDMA-Cl biotransformation was 0.09 μmol/[mg of volatile suspended solids (VSS)·h]. The Microtox acute toxicity EC(50) value of BDMA was 500 times higher than that of C(14)BDMA-Cl. Thus, the aerobic biotransformation of C(14)BDMA-Cl to BDMA results in substantial toxicity reduction. Phylogenetic analysis of Bacteria diversity indicated that the majority of the sequenced clones (98% of the clone library) belonged to the genus Pseudomonas.

Inhibition and biotransformation potential of naphthenic acids under different electron accepting conditions

Naphthenic acids (NAs) are a complex group of alkyl-substituted acyclic, monocyclic and polycyclic carboxylic acids present in crude oil, oil sands process water and tailings ponds, as well as in refinery wastewater. Bioassays were performed to investigate the biotransformation potential and inhibitory effect of a commercial NA mixture to nitrification, denitrification and fermentation/methanogenesis using mixed cultures not previously exposed to NAs. NAs inhibited nitrification in a mixed aerobic heterotrophic/nitrifying culture at concentrations as low as 80 mg NA/L, whereas, an enriched nitrifying culture was only affected at 400 mg NA/L. The lower nitrification inhibition in the latter assay is attributed to the higher population size of nitrosofying and nitrifying bacteria compared to the mixed heterotrophic/nitrifying culture. The NA mixture was not inhibitory to denitrifiers up to 400 mg/L. At higher NA concentrations, cell lysis was pronounced and lysis products were the main source of degradable carbon driving denitrification in culture series prepared without an external carbon source. In the presence of a degradable external carbon source, no difference was observed in nitrate reduction rates or nitrogen gas production at all NA concentrations tested. Methanogenesis was completely inhibited at NA concentrations equal to or higher than 200 mg/L. Methanogenic culture series amended with 80 mg NA/L were transiently inhibited and methane production in culture series prepared with NAs and an external carbon source or NAs only recovered in 136 and 41 days, respectively. Accumulation of volatile fatty acids was observed at inhibitory NA concentrations; however, carbon dioxide production was not affected by NAs, indicating that fermentation and acidogenesis were not affected by NAs. NAs were not degraded under nitrate-reducing or fermentative/methanogenic conditions used in the present study, regardless of the presence or not of another, degradable carbon/energy source.

Aerobic biotransformation potential of a commercial mixture of naphthenic acids

The biotransformation potential of a commercial naphthenic acid (NA) mixture (NA sodium salt; TCI Chemicals) under aerobic conditions was investigated using mixed aerobic cultures developed under various levels and duration of NA exposure. A culture enriched using the commercial NA mixture as the sole carbon source degraded NAs in a range of NA concentrations, regardless of culture age and the presence of a co-substrate; however, only 28.5% of the NA-carbon was detected as CO2 while 44% was utilized for biomass growth. A fraction of the NA mixture (15-26%) was persistent under all conditions studied. In contrast, a culture fed with a degradable synthetic wastewater only (NA un-amended culture) and another culture fed with the same wastewater and 50 mg NA/L (NA-amended culture), over time lost their ability to degrade NAs. Analysis of the 16S rRNA gene based clone library revealed that 80% of the NA-enriched culture belonged to the γ-Proteobacteria class and was largely dominated by phylotypes most closely related to known NA and hydrocarbon degraders such as Pseudomonas and Microbulbifer. The results of this study indicate that although significant NA degradation is possible, only a small fraction of the NA mixture is completely mineralized to CO2. Further investigation into the biotransformation products and conditions affecting NA biodegradation under realistic refinery and environmental conditions will help to design effective treatment and bioremediation processes.