The effect of thermal pretreatment on the anaerobic biodegradability and toxicity of waste activated sludge

The management of sludges generated by biological treatment of wastewaters has become an increasingly severe problem in recent years. The objective of this study was to examine the effect of thermochemical pretreatment on the anaerobic biodegradability and toxicity of waste activated sludge (WAS). In order to accomplish this, the degradability and toxicity of pure nitrogenous organic compounds present in WAS, and mixtures of these compounds, were also evaluated.The anaerobic bioconvertibility and toxicity of the various organics were determined using batch bioassay techniques. It was found that WAS bioconvertibility increased with increasing pretreatment temperature up to a maximum at 175°, and this resulted in an increase in methane production of 27% over the control. With the compounds and cultures used, mesophilic bioconvertibility and toxicity were found to be significantly higher than the corresponding values under thermophilic conditions. Finally, it was found that most of the pure individual nitrogen compounds and simple mixtures tested were quite biodegradable, although at the concentrations evaluated (20 gl⁻¹) most were toxic. It was also noted that small changes in structure could have a significant effect on both toxicity and bioconvertibility. In most cases thermochemical pretreatment of these individual compounds resulted in decreased bioconvertibility and increased toxicity.In conclusion it can be stated that thermochemical pretreatment enhances WAS bioconvertibility, while under identical treatment conditions, resulted in a considerable reduction in the bioconvertibility of individual nitrogen compounds and mixtures. This effect appears to be due to the conversion of biodegradable organics to refractory ones. Further, the toxicity of WAS after thermochemical pretreatment appears to be due to its solubilization, and conversion of these soluble products to toxic compounds under more extreme treatment conditions.     

Long-term effects of operating temperature and sulphate addition on the methanogenic community structure of anaerobic hybrid reactors

The diversity, population dynamics, and activity profiles of methanogens in anaerobic granular sludges from two anaerobic hybrid reactors treating a molasses wastewater both mesophilically (37 degrees C) and thermophilically (55 degrees C) during a 1081 day trial were determined. The influent to one of the reactors was supplemented with sulphate, after an acclimation period of 112 days, to determine the effect of competition with sulphate-reducing bacteria on the methanogenic community structure. Sludge samples were removed from the reactors at intervals throughout the operational period and examined by amplified ribosomal DNA (rDNA) restriction analysis (ARDRA) and partial sequencing of 16S rRNA genes. In total, 18 operational taxonomic units (OTUs) were identified, 12 of which were sequenced. The methanogenic communities in both reactors changed during the operational period. The seed sludge and the reactor biomass sampled during mesophilic operation, both in the presence and absence of sulphate, was characterised by a predominance of Methanosaeta spp. Following temperature elevation, the dominant methanogenic sequences detected in the non-sulphate supplemented reactor were closely related to Methanocorpusculum parvum. By contrast, the dominant OTUs detected in the sulphate-supplemented reactor upon temperature increase were related to the hydrogen-utilising methanogen, Methanobacterium thermoautotrophicum. The observed methanogenic community structure in the reactors correlated with the operational performance of the reactors during the trial and with physiological measurements of the reactor biomass. Both reactors achieved chemical oxygen demand (COD) removal efficiencies of over 90% during mesophilic operation, with or without sulphate supplementation. During thermophilic operation, the presence of sulphate resulted in decreased reactor performance (effluent acetate concentrations of >3000 mg/l and biogas methane content of <25%). It was demonstrated that methanogenic conversion of acetate at 55 degrees C was extremely sensitive to inhibition by sulphide (50% inhibition at 8-17 mg/l unionised sulphide at pH 7.6-8.0), while the conversion of H(2)/CO(2) methanogenically was favoured. The combination of experiments carried out demonstrated the presence of specific methanogenic populations during periods of successful operational performance.     

Anaerobic toxicity and biodegradability of pulp mill waste constituents

Batch bioassays have been conducted to characterize the response of methanogenic bacteria to several constituents of sulfite evaporator condensate. The results can be grouped into three ranges with increasingly severe consequences to anaerobic reactors: a low concentration, no effect range; a medium concentration range where methanogenesis is temporarily interrupted or slowed down, but may return to normal; and a high concentration range where methanogenesis is permanently inhibited. In some cases the toxicant was metabolized when present in the lower concentration ranges. There was also evidence that mechanisms other than fermentation to methane were significant in accounting for removal of the toxicants from solution. Organisms acclimated to low concentrations of a toxicant are better able to withstand a shock load of that toxicant than are unacclimated organisms.     

Psychrophilic and mesophilic anaerobic digestion of brewery effluent: a comparative study

Two expanded granular sludge bed-anaerobic filter (EGSB-AF) bioreactors (3.38 l active volume) were used to directly compare psychrophilic (15 degrees C), anaerobic digestion (PAD) to mesophilic (37 degrees C) anaerobic digestion (MAD) for the treatment of a brewery wastewater (chemical oxygen demand (COD) concentration of 3,136+/-891 mg l(-1)). Bioreactor performance was evaluated by COD removal efficiency and biogas yields at a range of hydraulic and organic loading rates. Specific methanogenic activity (SMA) assays were also employed to investigate the activity of the biomass in the bioreactors. No significant difference in the COD removal efficiencies (which ranged from 85-93%) were recorded between PAD and MAD during the 194-d trial at maximum organic and hydraulic loading rates of 4.47 kg m(-3) day(-1) and 1.33 m(3) m(-3) day(-1), respectively. In addition, the methane content (%) of the biogas was very similar. The volumetric biogas yield from the PAD bioreactor was approximately 50% of that from the MAD bioreactor at an organic loading rate of 4.47 kg COD m(-3) day(-3) and an applied liquid up-flow velocity (V(up)) of 2.5 m h(-1). Increasing the V(up) in the PAD bioreactor to 5 m h(-1) resulted in a volumetric biogas production rate of approximately 4.1 l d(-1) and a methane yield of 0.28 l CH(4) g(-1) COD d(-1), which were very similar to the MAD bioreactor. Significant and negligible biomass washout was observed in the mesophilic and psychrophilic systems, respectively, thus increasing the sludge loading rate applied to the former and underlining the robustness of the latter, which appeared underloaded. A psychrotolerant mesophilic, but not truly psychrophilic, biomass developed in the PAD bioreactor biomass, with comparable maximum SMA values to the MAD bioreactor biomass. PAD, therefore, was shown to be favourably comparable to MAD for brewery wastewater treatment and biogas generation.     

Bacterial populations and their roles in a pharmaceutical-waste anaerobic filter

The bacterial populations, their roles and distribution in an anaerobic filter treating a simulated pharmaceutical effluent containing a branched-chain fatty acid (BCFA) were studied. The BCFA degradation pathway and mechanisms were also investigated. The biofilm from the filter was enriched in serum bottle cultures using different BCFAs and fatty acids as the sole carbon source. The anaerobic biofilm was a consortium of (1) BCFA-degrading Syntrophomonas spp. which produced ethanoic acid and H₂, (2) H₂-utilizing Methanococcus spp. and (3) ethanoate-utilizing Methanothrix spp. Beta-oxidation was proposed as the acidogenic mechanism. The bacterial consortium could degrade BCFAs with tertiary carbon but not those with quaternary carbon. Branching at the alpha or beta position along the carbon chain interfered with the beta-oxidation mechanisms. Bacterial distribution in the filter was uneven, which was attributed to incomplete mixing.     

Quantitative image analysis as a diagnostic tool for identifying structural changes during a revival process of anaerobic granular sludge

Due to unspecified operational problems, the specific acetoclastic activity (SAA) of the anaerobic granular sludge present in an industrial UASB reactor was considerably damaged (from 250 to less than 10mL CH(4)@STP/gVSS.d), significantly reducing the biogas production of that industrial unit. The hydrogenotrophic methanogenic activity exhibited a value of 600mL CH4@STP/gVSS.d, the settling velocity was 31.4+/-9.8m/h, the average equivalent diameter was 0.92+/-0.43mm, and about 70% of the VSS were structured in aggregates larger than 1mm. In order to study the recovery of the SAA, this sludge was collected and inoculated in a lab-scale expanded granular sludge blanket (EGSB) reactor. Ethanol was fed as the sole carbon source during a trial period of 106 days. Process monitoring included COD removal efficiency, methane production, and periodic determination of the specific methanogenic activity in the presence of acetate, propionate, butyrate, ethanol and H(2)/CO(2). Quantitative image analysis allowed for information to be obtained on granular fragmentation/erosion and filaments release. During the first operational period, biogas production was mainly due to the hydrogenotrophic activity. However, after 40 days, the SAA steadily increased achieving a maximum value of 183+/-13mL CH4@STP/gVSS.d. The onset of SAA recovery, granules breakdown and filaments release to the bulk occurred simultaneously. Further increase in SAA was accompanied by granular growth. In the last 25 days of operation, the size distribution was stable with more than 80% of projected area of aggregates corresponding to granules larger than 1mm (equivalent diameter). Confocal images from FISH hybridized sections of the granules showed that after SAA recovery, the granules developed an organized structure where an acidogenic/acetogenic external layer was apparent. Granular fragmentation and increase of filaments in the bulk, simultaneously with the increase in the acetoclastic activity are described for the first time and might represent a structural response of granular sludge to promote the optimal substrate uptake at minimal diffusion limitations.     

Quantitative and qualitative analysis of methanogenic communities in mesophilically and psychrophilically cultivated anaerobic granular biofilims

Anaerobic granulation describes the self-immobilisation of methanogenic consortia into dense, particulate biofilms. This procedure underpins the operation of several categories of high-rate anaerobic wastewater treatment system. Full-scale anaerobic granular sludge plants have been generally operated in the mesophilic (20-45 °C) or thermophilic (45-65 °C) temperature range. On the other hand, recent studies highlighted the economic advantages of treating wastewaters at their discharge temperatures (mostly under 18 °C), removing a costly heating process and increasing net biogas yield. However, as yet, relatively little information is available about the microbial behaviour and interactions in anaerobic granular sludge formed under psychrophilic conditions. To this end, and in order to provide a microbial insight into low-temperature anaerobic granulation, we monitored the changes in methanogenic community structure, associated with the changes in process performance. Three, laboratory-scale, expanded granular sludge bed (EGSB) bioreactors treating a synthetic glucose wastewater were tested at two temperatures of 37 ± 1 °C (R1) and 15 ± 1 °C (R2 and 3). Quantitative real-time PCR and specific methanogenic activity assays highlighted a community shift towards hydrogenotrophic methanogens, particularly the order Methanomicrobiales in the low-temperature bioreactors. Corresponding to this, denaturing gradient gel electrophoresis (DGGE) analysis identified the emergence and maintenance of a Methanocorpusculum-like organism. Our results indicate that hydrogenotrophic methanogens, particularly the Methanomicrobiales-related populations, are likely to play important roles in low-temperature anaerobic granular sludge systems. This suggests that the process efficiency could be improved by facilitating the growth and retention of this group.     

Biodegradability and toxicity of sulphonate-based surfactants in aerobic and anaerobic aquatic environments

Four types of commonly used sulphonate-based surfactants (alkane sulphonates, alpha-olefin sulphonates, sulphosuccinates and methyl ester sulphonates) were tested for their aerobic and anaerobic biodegradability as well as for their toxicity to Daphnia magna and Photobacterium phosphoreum to assess the effect of the surfactant structure on those properties. Aerobic biodegradation was evaluated by means of the CO₂ headspace test and anaerobic biodegradation was assessed by a method based on the ECETOC test. All the surfactants tested were readily biodegraded under aerobic conditions. No clear effect of the surfactant structures on the toxicity to the aquatic organisms tested was found. The most significant differences in the surfactants studied were observed in their behaviour under anaerobic conditions. Alkane sulphonates, alpha-olefin sulphonates and methyl ester sulphonates were not mineralized in lab anaerobic digesters despite the fact that the last one showed a certain degree of primary degradation. Nevertheless, these surfactants did not significantly inhibit methanogenic activity at concentrations up to 15 g surfactant/kg dry sludge, a concentration that is much higher than the expected concentrations of these surfactants in real anaerobic digesters. Sulphosuccinates showed a high level of primary biodegradation in anaerobic conditions. However, linear alkyl sulphosuccinates were completely mineralized whereas branched alkyl sulphosuccinates achieved percentages of ultimate biodegradation ≤50%.     

Fate and effects of semivolatile organic pollutants during anaerobic digestion of sludge

Anaerobic digestion of primary and secondary sludge containing selected semivolatile organic pollutants was investigated. Typical digester operation was simulated with three, complete-mix, bench-scale digesters maintained at 35.5°C with a 30 day solids retention time. Two digesters were fed a primary and secondary sludge mixture produced from wastewater spiked with twenty semivolatile organics from the CERCLA pollutant list. The remaining digester (the control) was fed a similar mixture of sludge, but with no added organics. Operational parameters were monitored to compare the test and control units. All parameters were found to be within the limits of normal operation. Performance was near identical. An isotope dilution GC/MS method was employed for organics analysis of influent and effluent streams for all reactors. Steady-state fates of the organics were determined by mass balance. Twelve of the chemicals appear consistently and at steady state. Degradation was apparent for all components, with at least 10% of each parent compound partially or completely transformed. Sorption onto digester solids was an important removal mechanism. Results of organic analysis for the control digester highlight the effects of metabolic interferences.     

Long-term (1243 days), low-temperature (4-15 °C), anaerobic biotreatment of acidified wastewaters: Bioprocess performance and physiological characteristics

The feasibility of long-term (>3 years), low-temperature (4-15 °C) and anaerobic bioreactor operation, for the treatment of acidified wastewater, was investigated. A hybrid, expanded granular sludge bed-anaerobic filter bioreactor was seeded with a mesophilic inoculum and employed for the mineralization of moderate-strength (3.75-10 kg chemical oxygen demand (COD) m⁻³) volatile fatty acid-based wastewaters at 4-15 °C. Bioprocess performance was assessed in terms of COD removal efficiency (CODRE), methane biogas concentration, and yield, and biomass retention. Batch specific methanogenic activity assays were performed to physiologically characterise reactor biomass.Despite transient disimprovements, CODRE and methane biogas concentrations exceeded 80% and 65%, respectively, at an applied organic loading rate (OLR) of 10 kg COD m⁻³ d⁻¹ between 9.5 and 15 °C (sludge loading rate (SLR), 0.6 kg COD kg[VSS]⁻¹ d⁻¹). Over 50% of the granular sludge bed was lost to disintegration during operation at 9.5 °C, warranting a reduction in the applied OLR to 3.75-5 kg COD m⁻³ d⁻¹ (SLR, c. 0.4-0.5 kg COD kg[VSS]⁻¹ d⁻¹). From that point forward, remarkably stable and efficient performance was observed during operation at 4-10 °C, with respect to CODRE (≥82%), methane biogas concentration (>70%) and methane yields (>4 l_Methane d⁻¹), suggesting the adaptation of our mesophilic inoculum to psychrophilic operating conditions.Physiological activity assays indicated the development of psychroactive syntrophic and methanogenic populations, including the emergence of putatively psychrophilic propionate-oxidising and hydrogenotrophic methanogenic activity. The data suggest that mesophilic inocula can physiologically adapt to sub-optimal operational temperatures: treatment efficiencies and sludge loading rates at 4 °C (day, 1243) were comparable to those achieved at 15 °C (day 0). Furthermore, long-term, low-temperature bioreactor operation may act as a selective enrichment for psychrophilic methanogenic activity from mesophilic inocula. The observed efficient and stable bioprocess performance highlights the potential for long-term, low-temperature bioreactor operation.     

The anaerobic digestion of surplus activated sludge in a fixed-film bioreactor

It is necessary to identify the best operating conditions of the reactor to achieve a satisfactory performance of an anaerobic digester.This paper discusses the performance of a particular fixed-film bioreactor with sponges as support. This evaluation was made at laboratory scale through a comparison between a fixed-film bioreactor and a conventional continuous stirred tank reactor (CSTR).The results show good reactor productivity as well as satisfactory sludge stabilization.     

Influence of high NaCl and NH4Cl salt levels on methanogenic associations

The effect of high levels of NaCl and NH₄Cl on the activity and attachment of methanogenic associations in semi-continuous flow-through reactor systems has been evaluated. Two well-functioning reactors received shock concentrations of NaCl and NH₄Cl while two other reactors were adapted to increasing levels of the salts during a period of 45 days. The methanogenic associations, grown on a medium containing mainly acetate and ethanol, were found to be more resistant to NaCl and NH₄Cl than previously reported. Initial inhibition occurred at shock treatments of 30 gl⁻¹ for both salts. The reactors which were gradually exposed to increasing levels of the salts, adapted well and their tolerance levels surpassed those of the non-trained counterparts. Initial inhibition and fifty percent inhibition was observed at 65 and 95 gl⁻¹ respectively for adaptation to NaCl. Initial inhibition for the reactor adapting to NH₄Cl occurred at 30 gl⁻¹ and a 50% inhibition was observed at 45 gl⁻¹ of NH₄Cl. For the reactors receiving NH₄Cl, the free ammonia-N should be kept below a concentration of 80–100 mg l⁻¹ for optimal performance. The bacterial populations in the reactors consisted mostly out of Methanosarcina (> 99% of the biomass)     

The anaerobic degradation of detergent range fatty alcohol ethoxylates. Studies with C-labelled model surfactants

The anaerobic degradation of fatty alcohol polyglycol ethers was studied in a model sludge digester employing stearyl alcohol ethoxylate which was ¹⁴C-labelled either in the alkyl or in the heptaglycol chain. After 4-weeks' incubation of the ¹⁴C-compounds at 35°C in the presence of raw sludge as additional digestible substrate more than 80% of the initial radioactivity was found as methane and carbon dioxide. In addition, the major part of radioactivity in the digested sludge, corresponding to nearly 10% of added ¹⁴C, was attributable to biomass so that ultimate degradation of the two model surfactants amounted to more than 90%. Analysis of the small fraction of radiolabelled metabolites in the sludge supernatant allowed conclusions with regard to the anaerobic degradation route of linear alcohol ethoxylates. After primary biodegradation of the surfactant molecule by scission into the alkyl and poly(ethylene glycol) moieties the further biodegradation of the latter seems to proceed as under aerobic conditions, i.e. via oxidative or hydrolytic depolymerization steps. Eventually, ultimate biodegradation of the obtained monomers (C₂-units) leads to the formation of the gaseous end products.     

Treatment of phenol and cresols in upflow anaerobic sludge blanket (UASB) process: a review

Upflow anaerobic sludge blanket (UASB) process has been successfully applied in the treatment of municipal and industrial wastewaters. Several researchers have investigated the suitability of the process for the treatment of phenols and phenolic wastewaters. The anaerobic treatment of phenols is still at an investigative stage. With increasing recognition of the UASB process, feasibility studies on the treatment of wastewater containing phenol and cresols (o-, m- and p- isomers) in UASB have been reviewed. It is reported that phenol concentration up to a range of 500-750 mg/L is generally not inhibitory to the UASB process. Phenol concentrations greater than 500 mg/L can be effectively treated with acclimatization of inocula, recirculation of the treated effluent and/or supplementing with co-substrates such as glucose, VFA and dilute molasses. The degradability of phenol is more than p-cresol, which in turn is more than m- and o-cresol.     

The influence of growth medium composition on the toxicity of chemicals to algae

Algal growth inhibition tests are an important part of monitoring programmes designed to predict the environmental impact of new substances. This study investigated the effects of varying growth medium composition on the toxicity of four chemicals (morpholine, nitrilotriacetic acid, o-dichlorobenzene and triphenyl phosphate) to three species of freshwater green algae recommended for use in standard algal growth inhibition tests: Selenastrum capricornutum, Scenedesmus subspicatus and Chlorella vulgaris. Bold's basal, OECD and EPA media were used. The toxic values obtained from the tests suggest that medium composition significantly affected the sensitivity of the test algae to the four chemicals, but not in a predictable fashion.     

Anaerobic treatability of selected organic toxicants in petrochemical wastes

The objective of this research was to study the biodegradability of ethylene glycol, acrylic acid, acrolein and allyl alcohol using a methanogenic acetate enrichment culture. Anaerobic Toxicity Assays (ATA) and Biochemical Methane Potential (BMP) studies were performed with serum bottles. Ethylene glycol was found to be degraded to less than 5 mg/l with spikes up to 10,000 mg/l. Higher concentrations led to pH inhibition even with a design initial bicarbonate alkalinity of 6000 mg/l as CaCO₃. Acrylic acid was degraded with almost no effect on methanogens with spikes up to 100 mg/l. However, concentrations of 500, 1000 and 1500 mg/l were found to inhibit the methanogens for several days before recovery. Acrylic acid was eventually degraded to less than 1 mg/l in all cases. Acrolein was inhibitory at concentrations as low as 10 mg/l. However, recovery of the culture was observed at concentrations up to 150 mg/l. Allyl alcohol was cometabolized when acetate was supplied to the bottles in the ATA; it was not degraded well when supplied as the sole carbon source in the BMP study. Ethylene glycol and acrylic acid were found to be suitable for anaerobic treatment whereas allyl alcohol and acrolein were not suitable at the selected concentrations using a methanogenic culture.     

Bioaccumulation and toxicity of copper as affected by interactions between humic acid and water hardness

This study evaluated the effects of water hardness and humic acid (HA) on the acute and chronic toxicity of copper to Daphnia pulex and on its accumulation by D. magna. Hardness had little effect on either the acute (3-day) or the chronic (42-day) toxicity of copper. Humic acid significantly reduced both the acute and chronic toxicity of copper when added to waters having hardnesses of 58, 115 and 230 mg l^?1 as CaCO₃. The effect, per unit of HA, on chronic toxicity was very similar for soft and medium water but less in hard water. At each of two HA concentrations, copper was chronically more toxic in hard water than in either medium or soft water. Bioaccumulation of copper varied with relative hardness and HA concentration and this was further affected by age at exposure. For 1-day-old animals, an increase in either hardness or HA- or any combination of the two, tended to decrease bioaccumulation. Results for 7-day-old animals were in general agreement except for animals exposed to copper in hard water at an intermediate HA concentration. These animals accumulated significantly more copper in the presence of HA. This agrees with the fact that this concentration of HA also increased the chronic toxicity of copper in hard water. Both of those phenomena are probably due to the displacement of Cu²⁺ from HA by competition from the increased concentrations of Ca²⁺ and Mg²⁺. The fact that HA had the opposite effect on copper accumulation by young animals in hard water could not be explained.     

火灾烟气毒性评价新的"RRC"动态模型及工程应用

就火灾中的死亡人数而言，最主要的威胁来自于火灾中的烟气。目前已经有很多种模型来描述火灾中的烟气毒性危害，如CO随机模型、FED、FEC和N气体模型。所有这些模型都不能反应真实火灾中烟气浓度的时空变化。根据真实火灾中的烟气危害度，选取人员的呼吸率、人员在火灾中的逃生路径、特定建筑中的烟气浓度场分布等三个对于人员致死具有决定性的因素，初步建立一个新的“RRC”动态模型来描述火灾中的烟气毒性危害，并通过算例展示了模型的工程应用。     

Mitigating ammonia inhibition of thermophilic anaerobic treatment of digested piggery wastewater: use of pH reduction, zeolite, biomass and humic acid

High free ammonia released during anaerobic digestion of livestock wastes is widely known to inhibit methanogenic microorganisms and result in low methane production. This was encountered during our earlier thermophilic semi-continuously fed continuously-stirred tank reactor (CSTR) treatment of piggery wastewater. This study explored chemical and biological means to mitigate ammonia inhibition on thermophilic anaerobic treatment of piggery wastewater with the aim to increase organic volatile carbon reduction and methane production. A series of thermophilic anaerobic batch experiments were conducted on the digested piggery effluent to investigate the effects of pH reduction (pH 8.3 to 7.5, 7.0 and 6.5) and additions of biomass (10% v/v and 19% v/v anaerobic digested piggery biomass and aerobic-anaerobic digested municipal biomass), natural zeolite (10, 15 and 20 g/L) and humic acid (1, 5 and 10 g/L) on methane production at 55 °C for 9-11 days. Reduction of the wastewater pH from its initial pH of 8.3 to 6.5 produced the greatest stimulation of methane production (3.4 fold) coupled with reductions in free ammonia (38 fold) and total volatile fatty acids (58% TVFA), particularly acetate and propionate. Addition of 10-20 g/L zeolite to piggery wastewater with and without pH reduction to 6.5 further enhanced total VFA reduction and methane production over their respective controls, with 20 g/L zeolite producing the highest enhancement effect despite the ammonia-nitrogen concentrations of the treated wastewaters remaining high. Without pH reduction, zeolite concentration up to 20 g/L was required to achieve comparable methane enhancement as the pH-reduced wastewater at pH 6.5. Although biomass (10% v/v piggery and municipal wastes) and low humic acid (1 and 5 g/L) additions enhanced total VFA reduction and methane production, they elevated the residual effluent total COD concentrations over the control wastewaters (pH-unadjusted and pH-reduced) unlike zeolite treatment. The outcomes from these batch experiments support the use of pH reduction to 6.5 and zeolite treatment (10-20 g/L) as effective strategies to mitigate ammonia inhibition of the thermophilic anaerobic treatment of piggery wastewater.     

The effects of phenol and some alkyl phenolics on batch anaerobic methanogenesis

Phenol and seven alkylphenols (o-, m- and p-cresol, 2.5-, 2.6-, 3.4- and 3,5-dimethylphenol) were added at various concentrations to aliquots of domestic anaerobic sludge in Hungate serum bottles and these were incubated at 37°C. The concentration of methane in the headspace gas was monitored to determine if the phenolics were fermented to methane or if they inhibited the anaerobic process. Only phenol and p-cresol were fermented to methane. At 500 mg l⁻¹ (but not at 300 mg l⁻¹) 2,5-, 3,4- and 3,5-dimethylphenol reduced the rate and the amount of methane produced. The cresols were inhibitory at 1000 mg l⁻¹ but not at 400 mg l⁻¹.In cultures supplemented with acetate and propionate (VOA), and in unsupplemented cultures, phenol at concentrations up to 500 mg l⁻¹ was fermented to methane. Between 800 and 1200 mg l⁻¹ phenol, methane production was neither enhanced nor inhibited relative to control cultures containing no phenol. Inhibition of methane production was evident when phenol was present at 2000 mg l⁻¹. Thus the methanogens are less susceptible to phenol inhibition than are the phenol-degrading acid formers. In similar experiments with p-cresol: enhanced methane production was observed at concentrations of 400 mg l⁻¹; no enhancement or inhibition was observed at 600 mg l⁻¹; and inhibition was noted when p-cresol was present at 1000 mg l⁻¹.