Fermentation Of Sewage Sludge Research Articles

The effects of headspace volume reactor on the microbial community structure during fermentation processes for volatile fatty acid production.

The transition from traditional wastewater treatment plants to biorefineries represents an environmentally and economically sustainable approach to extracting valuable compounds from waste. Sewage sludge produced from wastewater treatment is incinerated or disposed of in specific landfills. Repurposing this waste material to recover valuable resources could help lower disposal costs and reduce environmental impact by producing other beneficial polymers. Microorganisms present in the sewage sludge can ferment organic pollutants, producing volatile fatty acids (VFA), precursors for biopolymers that could be used as an alternative to petroleum-derived plastics. To boost VFA production during sewage sludge fermentation, it is necessary to understand the operating microbial community and its metabolic capacities in anaerobic conditions. This study presents the influence of the headspace volume on the microbial community and the VFA production to define the best operational parameters in a 225 L pilot plant fermenter. The wasted sewage sludge was withdrawn from an oxic-settling-anaerobic plant that collected wastewater from the canteen and dormitory of the UNIPA Campus (Palermo University, Italy) and incubated using a 40% and a 60% headspace volume. The microbial community was analysed before and after the fermentation process through metataxonomic analysis, and VFA yields were determined by gas chromatography analysis. Our results showed that the 40% headspace volume induced a tenfold higher VFA production than the 60% headspace volume, modulating the microbial community's efforts to establish a VFA-producing factory. Notably, at 40% headspace, the relative abundance of bacteria, like Proteobacteria, Firmicutes, Actinobacteria, and Chloroflexi, significantly increased, as well as the relative abundance of Bacteroidetes and Verrucomicrobia decreased during the fermentation process. This result is consistent with the selection of efficient VFA-producing bacteria that lead to increased VFA yields that are not obtained at 60% headspace. Thus, reducing headspace is a promising strategy that can be implemented, even in full-scale plants, to optimise the wastewater reuse process and maximise VFA production to produce bioplastics, like polyhydroxyalkanoate, for the transition from linear wastewater treatment plants to circular biorefineries.

Assessing the aerobic/anoxic enrichment efficiency at different C/N ratios: pilot scale polyhydroxyalkanoates production from waste activated sludge

Polyhydroxyalkanoates (PHA) can be produced using fermentation products of an excess sewage sludge fermentation process. An efficient method to enrich a PHA-producing community is an aerobic-feast/anoxic-famine enrichment strategy. The effect of different carbon to nitrogen (C/N) feed ratios of 1, 2 and 3.5 g COD/g N on the process performance was studied. The study was executed on a pilot plant scale using fermented waste activated sludge as the organic carbon source. The system's performance was monitored in terms of removing contaminants, producing PHA, and reducing N2O emissions. The results indicated that a lower C/N ratio results in lower PHA production, with PHA content in the sludge of 20, 24 and 36 % w/w for C/N ratios of 1, 2 and 3.5 g COD/g N, respectively. At the lowest C/N ratio, the highest nitrite accumulation rate (77%), nitrification efficiency (89%) and denitrification efficiency (89%) were observed, but the N2O production was also the highest (0.77 mg N2O-N/L). The long-term comprehensive monitoring carried out in this study revealed high carbon and ammonia removal efficiencies (never below 80%) despite the C/N shifts and high COD and ammonia concentrations. At the same time, the system showed relatively low PHA production and high environmental impact in terms of high gaseous N2O emission. These findings question the sustainability of the aerobic-feast/anoxic-famine enrichment strategy for PHA production in full-scale plants.

Impact of thermal hydrolysis on VFA-based carbon source production from fermentation of sludge and digestate for denitrification: experimentation and upscaling implications

Stricter nutrient discharge limits at wastewater treatment plants (WWTPs) are increasing the demand for external carbon sources for denitrification, especially at cold temperatures. Production of carbon sources at WWTP by fermentation of sewage sludge often results in low yields of soluble carbon and volatile fatty acids (VFA) and high biogas losses, limiting its feasibility for full-scale application. This study investigated the overall impact of thermal hydrolysis pre-treatment (THP) on the production of VFA for denitrification through the fermentation of municipal sludge and digestate. Fermentation products and yields, denitrification efficiency and potential impacts on methane yield in the downstream process after carbon source separation were evaluated. Fermentation of THP substrates resulted in 37–70 % higher soluble chemical oxygen demand (sCOD) concentrations than fermentation of untreated substrates but did not significantly affect VFA yield after fermentation. Nevertheless, THP had a positive impact on the denitrification rates and on the methane yields of the residual solid fraction in all experiments. Among the different carbon sources tested, the one produced from the fermentation of THP-digestate showed an overall better potential as a carbon source than other substrates (e.g. sludge). It obtained a relatively high carbon solubilisation degree (39 %) and higher concentrations of sCOD (19 g sCOD/L) and VFA (9.8 g VFACOD/L), which resulted in a higher denitrification rate (8.77 mg NOx-N/g VSS∙h). After the separation of the carbon source, the solid phase from this sample produced a methane yield of 101 mL CH4/g VS. Furthermore, fermentation of a 50:50 mixture of THP-substrate and raw sludge produced also resulted in a high VFA yield (283 g VFACOD/kg VSin) and denitrification rate of 8.74 mg NOx-N/g VSS∙h, indicating a potential for reduced treatment volumes. Calculations based on a full-scale WWTP (Käppala, Stockholm) demonstrated that the carbon sources produced could replace fossil-based methanol and meet the nitrogen effluent limit (6 mg/L) despite their ammonium content. Fermentation of 50–63 % of the available sludge at Käppala WWTP in 2028 could produce enough carbon source to replace methanol, with only an 8–20 % reduction in methane production, depending on the production process. Additionally, digestate production would be sufficient to generate 81 % of the required carbon source while also increasing methane production by 5 % if a portion of the solid residues were recirculated to the digester.

Enhancing volatile fatty acid production in batch test reactors by modulating microbial communities with potassium permanganate

The shift from conventional wastewater treatment plants to biorefineries is one of the most environmentally and economically sustainable pathways for extracting valuable compounds from waste. Besides chemical-physical processes, microorganisms within sewage sludge utilize organic and inorganic pollutants in the wastewater as nutrients, leading to effective water purification. However, the remaining solid sludge residue, typically destined for specific landfills or incineration, could undergo microbial fermentation to produce volatile fatty acids (VFA), metabolic precursors for biopolymers. Increasing attention has been directed towards optimizing operational parameters to enhance VFA production during sewage sludge fermentation. This study examined the impact of potassium permanganate (PP) on microbial communities during the sewage sludge's acidogenic fermentation. The results highlighted the positive effect of PP treatment, which increased COD production and VFA yield up to 1263.5 mg/L and 664.2 mg COD/L, respectively. The presence of PP significantly enhances VFA yield promoting bacteria positively linked to VFA production.

Chlorine-free Extractions of Mixed-Culture Polyhydroxyalkanoates Produced from Fermented Sewage Sludge at Pilot Scale

Chlorine-free Extractions of Mixed-Culture Polyhydroxyalkanoates Produced from Fermented Sewage Sludge at Pilot Scale

Separation of nutrients and acetate from sewage sludge fermentation liquid in flow-electrode capacitive deionization system: Competitive mechanisms of ions and influence of activated carbon

Effective separation of volatile fatty acids (VFAs), ammonia (NH4+-N) and reactive phosphorous (RP) generated from anaerobic fermentation liquid is critically important for efficient resource recovery. Flow-electrode capacitive deionization (FCDI) is proven to be capable of efficient removal of ions, environmentally friendly and cost-effective in operation. The performances of FCDI system in the separation of NH4+-N, RP, and acetate and mechanism of pHs and activated carbon on their performances were investigated. Results showed that a pH of 5.0 promoted the removal of NH4+-N (53.1 %) and RP (39.5 %), and 72.0 % of acetate was retained in the solution, which revealed that removal of NH4+-N and RP, and retention of acetate were evidently affected by speciation of ions. Furthermore, the recovery of NH4+-N and RP was undermined by the adsorption of ions on activated carbon. This study provides a novel insight of ion selective mechanism during the operation of the FCDI system.

Mitigation of N2O emissions via enhanced denitrification in a biological landfill leachate treatment using external carbon from fermented sludge

The effects of an external carbon source (C-source) on the mitigation of N2O gas (N2O(g)) emissions from landfill leachate were investigated via enhanced denitrification using anaerobically fermented sewage sludge. Anaerobic fermentation of sewage sludge was conducted under thermophilic conditions with progressively increasing organic loading rates (OLR). Optimal conditions for fermentation were determined based on the efficiency of hydrolysis and the concentrations of sCOD and volatile fatty acids (VFAs) as follows: at an OLR of 40.48 ± 0.77 g COD/L·d with 1.5 days of solid retention time (SRT), 14.68 ± 0.59% of efficiency of hydrolysis, 14.42 ± 0.30 g sCOD/L and 7.85 ± 0.18 g COD/L of VFAs. Analysis of the microbial community in the anaerobic fermentation reactor revealed that degradation of sewage sludge might be potentially affected by proteolytic microorganisms producing VFAs from proteinaceous materials. Sludge-fermentate (SF) retrieved from the anaerobic fermentation reactor was used as the external C-source for denitrification testing. The specific nitrate removal rate (KNR) of the SF-added condition was 7.54 mg NO3−N/g VSS·hr, which was 5.42 and 2.43 times higher than that of raw landfill leachate (LL) and a methanol-added condition, respectively. In the N2O(g) emission test, the liquid phase N2O (N2O–N(l)) of 20.15 mg N/L was emitted as N2O(g) of 19.64 ppmv under only LL-added condition. On the other hand, SF led to the specific N2O(l) reduction rate (KN2O) of 6.70 mg N/g VSS hr, resulting in mitigation of 1.72 times the N2O(g) emission compared to under the only-LL-added condition. The present study revealed that N2O(g) emissions from biological landfill leachate treatment plants can be attenuated by simultaneous reduction of NO3−N and N2O(l) during enhanced denitrification via a stable supply of an external C-source retrieved from anaerobically fermented organic waste.

Ultrasonic-assisted hypochlorite activation accelerated volatile fatty acids production during sewage sludge fermentation: Critical insights on solubilization/hydrolysis stages and microbial traits

The effective disruption of extracellular polymeric substances using appropriate pretreatment is critical to achieving resource recovery from sewage sludge (SS) by anaerobic fermentation. This work proposed an ultrasonic-assisted hypochlorite activation strategy for enhanced production of volatile fatty acids (VFAs) during SS fermentation. The results demonstrated that after individual ultrasonic and hypochlorite pretreatment, the maximum VFAs yield improved by 8 and 107% with that in control, respectively, while a combination of both techniques led to an improvement of 119%, indicating their synergistic effects on SS fermentation. This method enhanced the solubilization and hydrolysis efficiencies and contributed to the increased biodegradable substrates, which would be beneficial in enhancing microbial activity for VFAs production. The functional anaerobes, metabolic pathways, and gene expressions involved in VFAs biosynthesis were effectively improved. This work would bring a novel insight into the disposal of municipal solid waste for resource recovery.

Increasing of efficiency of fermentation process of organic substrates for intensification of methanogeneration

The prospects of increasing the efficiency of fermentation process of organic substrates to ensure the maximum yield of biogas and increase the economic efficiency of processing of organic sewage sludge are considered. Biogas, as an analogue of natural gas, is used in production of thermal and electrical energy, as transport motor fuel, as a raw material for chemical industry.
 An analysis of trends in intensification of methane fermentation processes was carried out. A promising way to increase productivity of methane generation process during processing of organic matter is to increase the energy saturation of an organic substrate and its preliminary treatment. One of the approaches aimed at intensifying methane generation is use of organic waste as an auxiliary substrate for fermentation of sewage sludge – a process known as co-fermentation.
 The sediments of primary and secondary settling tanks of the biological wastewater treatment complex were studied. According to results of tests, it was noted that ratio of carbon and nitrogen in the studied excess activated sludge is 4–5, in the mixture of primary and secondary sediment – 5–6, in sediment from sludge sites – 6–10, which is significantly less than desired ratio of 20:1, which limits the negative impact of increased nitrogen content in the organic substrate for methane fermentation. According to obtained data, it can be predicted that nitrogen-containing compounds present in sewage sludge will contribute to a microbiological process of formation of nitrogen-containing reduced products, which reduce output of methane during methanogenesis.
 The expediency of enriching the inoculated biocenosis with hydrolytic enzyme preparations or microorganisms with high hydrolytic activity is shown, given the fact that activated sludge has a lower hydrolytic activity than enzyme preparations isolated from the same sludge, as well as than some bacteria, and even more so microscopic fungi. This was caused by presence of inert organic and inorganic mass, dead microorganisms and those with low hydrolytic activity in the sludge biomass. It is also possible to increase speed of the first phase of sediment fermentation due to alkaline pretreatment of the substrate mixture.

Zero valent iron catalyzing sulfite improves the quality and quantity of short-chain fatty acids from anaerobic fermentation of sewage sludge

The quality and quantity of short chain fatty acids (SCFAs) production from anaerobic fermentation of sewage sludge is generally constrained by low organics solubilization and poor substrate-availability. This study provided an environmentally friendly strategy with zero valent iron (ZVI) activating sulfite pretreatment to overcome this limitation and advance the sludge anaerobic fermentation. Experimental results showed that the maximal SCFAs production and acetate proportion promoted by 5.7 and 2.75 times respectively at 500 mg S/L and the ZVI/sulfite ratio of 1.25. Mechanism analysis elucidated that the free radicals of SO4-· and ·OH produced from ZVI-sulfite pretreatment accelerated the disintegration of sludge-flocs and decreased the value of α-helix and ratio of α-helix/ (β-sheet + random coil) from 21.64 % and 44.23 % to 17.80 % and 38.67 %, respectively, which provided more easily- and bio- available substance for functional anaerobes. The ZVI-sulfite pretreatment enhanced the ability of functional anaerobes for SCFAs production processes as hydrolysis, acidogenesis and acetogenesis and reduced the SCFAs consumption as methanogenesis, which ultimately promoted SCFAs accumulation. Microbial community illustrated that ZVI-sulfite pretreatment enriched the relative abundance of functional anaerobes related to hydrolysis, acidogenesis and acetogenesis bioprocesses. PICRUSt analysis demonstrated that the pretreatment boosted the functional genes abundance involved in pathway of butyrate and acetate formation. Moreover, the enrichment genes of acetate formation were consistent with the increase of acetate proportion.

Effect of the hydraulic retention time on the acidogenic fermentation of sewage sludge, wine vinasse and poultry manure for biohydrogen production

The present work aims to study the performance of the co-fermentation of sewage sludge, wine vinasse and poultry manure to generate volatile fatty acids (VFA) and biohydrogen at different hydraulic retention times (HRT: 10, 8, 6, 5 and 3 days). The study was carried out in constant agitated reactors at laboratory scale. The feeding consisted of a mixture of sludge:vinasse (50:50) with 10 g/L of poultry manure. The reactors operated under thermophilic conditions (55 °C) and pH of 5.5.The results showed an increase in hydrogen production and specific hydrogen production, 1.18LH2/L/d and 40.41 mLH2/gVSadded respectively, as HRT decreased from 10 to 5 days of HRT. The volatile solids (VS) removal (33.32%VSr) and 71.24% soluble chemical oxygen demand (SCOD) were observed at HRT of 5 days, with the highest butyric acid/acetic acid ratio (HBu/HAc) value of 2.09. As HRT drops below 5 days, yields and hydrogen production drop. The highest activity of the microorganisms was observed for a HRT of 5 days (5.64E-11 LH2/Cells), with a higher proportion of Eubacteria than Archaea (74:26) and higher concentration of Butyrate-utilizing Acetogens (BUA) than Propionate-utilizing Acetogens (PUA) (18.60 and 12.18% respectively). Therefore, this technology, in a 5-day HRT, could be a viable alternative for the production of bioenergy in the biorefinery concept.

Upgrading volatile fatty acids production from anaerobic co-fermentation of orange peel waste and sewage sludge: Critical roles of limonene on functional consortia and microbial metabolic traits

Orange peel waste (OPW) and sewage sludge (SS) valorization for volatile fatty acids (VFAs) production from anaerobic co-fermentation are attractive and feasible. The highest VFAs reached 11996.3 mg COD/L within 10 d at the mass ratio (TS/TS) of 1:1, which was approximately 30-fold of that in sole SS fermentation. The OPW provided plenty of organic substrates and facilitated the fermentation processes by disintegrating SS structure and inhibiting methanogenesis due to the abundant limonene. Also, the OPW feeds reshaped the microbial community and enriched fermentative bacteria, especially those saccharolytic ones (i.e. Prevotella-7). The key genes involved in membrane transport (i.e. ptsG), glycolysis (i.e. pgk), pyruvate metabolism (i.e. ace), and fatty acid biosynthesis (i.e. accA), which are associated with VFAs biosynthesis, were up-regulated in OPW/SS reactors. Overall, it was the increase in bioavailable organic matter and functional microorganisms, and the simultaneous enhancement of metabolic activity that improved the efficient VFAs production.

Simultaneous enhancing phosphorus recovery and volatile fatty acids production during anaerobic fermentation of sewage sludge with peroxydisulfate pre-oxidation

Phosphorus release and sludge hydrolysis are the keys for phosphorus and carbon recovery from sewage sludge via anaerobic process. In this study, iron-rich sludge (a common phosphorus-rich sewage sludge) was pre-oxidized by heat-activated peroxydisulfate (PDS) to enhance volatile fatty acids (VFAs) production and iron-bound phosphorus (Fe-P) release during anaerobic fermentation (AF). With low-dosage PDS pre-oxidation (33.75 mg/g total solids), the concentration of recoverable phosphorus increased by 49.3% than that noted in control along with enhanced VFAs production after 4 days. This is mainly because PDS oxidation not only effectively disintegrated sludge, but also generated sulfate simultaneously. Sludge disintegration enhanced organic matter hydrolysis, promoting VFAs yield, while sulfate was reduced to sulfide during AF and precipitated with iron, leading to Fe-P release. The application of PDS pre-oxidation on iron-rich sludge could not only improve the resourcefulness of sludge but also reduce secondary pollution (sulfate or hydrogen sulfide).

Biochemical assays of potential methane to test biogas production from dark fermentation of sewage sludge and agricultural residues

This study aims to study the methane generation potential (BMP tests) of different samples from the dark acid fermentation of sewage sludge:wine vinasse, and sewage sludge:wine vinasse:poultry manure. Specifically, mixtures of sewage sludge (S) and wine vinasse (V) were used in a 50:50 ratio and mixtures of sewage sludge and wine vinasse with 10 g/L of poultry manure (PM) (50:50 + 10 g/L) (S:V + PM). The goal was to determine the effect of the high ammonia concentrations in poultry manure when was used as co-substrate in the anaerobic methanogenic degradation of sewage sludge and vinasse. Results obtained show that the addition of 10 g/L of poultry manure to the SV mixture improves the production of methane generation, reaching values of 166 mL of accumulated methane. The SVPM mixture shows the highest purification percentages, with 63.90% TCOD removal, 79.51% SCOD removal and a yield of 52.05 mLCH 4 /gSV added . The SVPM test showed a higher concentration of microorganisms during the BMP test, although the population of microorganisms for the SV test was doubled and presented greater activity with values of 2.27 versus 1.73E-11 LCH 4 /Cells. • Bio-Methane Potential with the dark acid fermentation from a Bio-Hydrogen potential. • Bio-methane potential with sewage sludge, wine vinasse and poultry manure. • Anaerobic codigestion of sewage sludge, wine vinasse and poultry manure. • Poultry manure improves methane production and yield. • Anaerobic tridigestion presents better results than anaerobic bidigestion.

Short-Chain Fatty Acids Production from Anaerobic Fermentation of Sewage Sludge: The Effect of Higher Levels Polyaluminium Chloride.

With the annual increase in the sludge production in China’s sewage treatment plants, the problem of sewage sludge treatment and disposal is becoming more and more serious. Anaerobic fermentation can convert complex organic matter in sewage sludge into short-chain fatty acid, hydrogen, methane and other resources and is an effective method for sewage sludge treatment and disposal. At the same time, sewage sludge often contains flocculants, which will inevitably affect the effect of anaerobic fermentation. As a high-performance flocculant, polyaluminum chloride (PAC) is widely used in wastewater treatment and sewage sludge dewatering processes. Previous studies indicated that lower levels of PAC inhibit the effect of the anaerobic fermentation process of sewage sludge; on the other hand, it is necessary to understand the effects of higher levels of PAC in anaerobically fermented sewage sludge. The results showed that higher levels (0.2–1 g Al/g total solids (TS)) of PAC could promote acid production from anaerobically fermented sewage sludge. Moreover, mechanism studies suggest that higher levels (0.2–1 g Al/g total solids (TS)) of PAC caused excessive adsorption of the charge on the surface of the sewage sludge colloid and reversed the charge. The sewage sludge colloid was stabilized again, which increases the concentration of soluble proteins, polysaccharides, and soluble extracellular polymers (S-EPS) in the fermentation broth, thereby improving the anaerobically fermented sewage sludge efficiency. The results provided from this study may act as technical reference and guidance for the engineering application of sewage sludge anaerobic fermentation.

Potassium ferrate pretreatment promotes short chain fatty acids yield and antibiotics reduction in acidogenic fermentation of sewage sludge

During the acidogenic fermentation converting waste activated sludge (WAS) into short-chain fatty acids (SCFA), hydrolysis of complex organic polymers is a limiting step and the transformation of harmful substances (such as antibiotics) during acidogenic fermentation is unknown. In this study, potassium ferrate (K2FeO4) oxidation was used as a pretreatment strategy for WAS acidogenic fermentation to increase the hydrolysis of sludge and destruct the harmful antibiotics. Pretreatment with K2FeO4 can effectively increase the SCFA production during acidogenic fermentation and change the distribution of SCFA components. With the dosage of 0.2 g/g TS, the maximum SCFA yield was 4823 mg COD/L, which is 28.3 times that of the control group; acetic acid accounts for more than 90% of the total SCFA. The higher dosage (0.5 g/g TS) can further increase the proportion of acetic acid, but inhibit the overall performance of SCFA production. Apart from the promotion of hydrolysis and acidogenesis, K2FeO4 pretreatment can also simultaneously oxidizes and degrades part of the antibiotics in the sludge. When the dosage is 0.5 g/g TS, the degradation efficacy of antibiotics is the most significant, and the contents of ofloxacin, azithromycin, and tetracycline in the sludge are reduced by 69%, 42%, and 50%, respectively. In addition, K2FeO4 pretreatment can also promote the release of antibiotics from sludge flocs, which is conducive to the simultaneous degradation of antibiotics in the subsequent biological treatment process.

ASPECTS REGARDING THE ENERGITICAL VALORIFICATION OF URBAN SLUDGE TREATMENT

This paper highlights through the issues addressed, the application aspects regarding the approach of the concept of recovery of sewage sludge from an urban wastewater treatment plant (SEAU), which is in a stage of technological expansion and modernization. Thus, it is considered the need to process the potential of biological mass generated by anaerobic stabilization in the SEAU, with a population of about 10,000 equivalent inhabitants, which requires on one hand, the technological design of activated sludge basins and on the other hand, the design of a sewage sludge fermentation tank, in order to produce biogas, necessary for its recovery for energy purposes.

Deciphering the key operational factors and microbial features associated with volatile fatty acids production during paper wastes and sewage sludge co-fermentation

This work explored the feasibility of paper waste (PW)/sewage sludge (SS) co-fermentation for volatile fatty acids (VFAs) production, and disclosed its correlation with the key operational parameters (i.e., pH and PW/SS ratio). The results indicated that the maximal VFAs was 251.55 mg COD/g TSS at optimal conditions, which was approximately 10-folds of sole SS fermentation. PW feeding contributed to the bioavailable substrates and C/N balance during co-fermentation process. The pH exhibited evident impacts on organics solubilization/hydrolysis, in which acidic pH was more beneficial for carbohydrates metabolism while alkaline pH was better for proteins. Under optimal operational conditions, the metabolic functions associated with VFAs production (i.e., substrate membrane transport, intracellular metabolism and VFAs biosynthesis) were up-regulated. Moreover, functional microorganisms (i.e., Saccharofermentans and Bacteroides) responsible for VFAs generation were enriched. This work provided an innovative approach to recovery valuable products from biowastes, and in-depth understandings of microbial features in PW/SS co-fermentation systems.

Accelerating acidogenic fermentation of sewage sludge with ash addition

A statistically designed range of tests was used in order to map the impact of time, temperature and pH on the acidogenic fermentation of sewage sludge with the addition of wood fly ash. The main factors investigated were temperature (35, 55 and 65 °C), pH (7, 8 and 8.5) and retention time (1, 2 and 4 days). The initial pH was adjusted by adding ash. Up to about a third of the volatile solids could be solubilized in less than two days retention time. Higher temperatures (55 and 65 °C) and adjusted pH (7 and 8) favored hydrolysis whereas fermentation producing organic acids was faster at lower temperatures (35 °C). Sludge hydrolysis occurred fast at 55 and 65 °C, reaching a solubilized total organic carbon (TOC) concentration of 3.84 g TOC L−1 after one day. Thermophilic conditions (55 and 65 °C) resulted in a lower volatile fatty acids (VFA) concentration compared to mesophilic conditions (35 °C). At 35 °C, the highest VFA concentration was measured after 4 days and initial pH 7 (10.0 ± 0.2 g COD L−1). This study showed the potential of using a waste stream to increase and hasten the hydrolysis of particulate organics, resulting in higher TOC solubilized in 2 days, while promoting a higher VFA production presented as g COD L−1.

Infuence of Selected Pharmaceuticals on Biogas Production in Mesophilic Anaerobic Fermentation

Abstract This article deals with pharmaceutical compounds as micropollutants in anaerobic digestion of sludge from waste water treatment plant (WWTP). Part of the work included the research into presence of pharmaceuticals in different types of waters. Description of anaerobic fermentation process is also important in terms of optimal conditions. The practical aim of the investigation was preparation of a model of anaerobic fermentation of sewage sludge, where influence of pharmaceuticals on mesophilic anaerobic digestion was monitored. Wash out of micropollutants from sludge in big semicontinuous anaerobic reactors was running since October 2013. The resulting non-adapted sludge from mesophilic reactor was used since March 2014 for pharmaceuticals tests in half-a-litre glass bottles with a septum cap. The compounds of interest were diclofenac, tramadol, ibuprofen, carbamazepine and amoxicillin and their concentration in the tested sludge was 10 μg/L and 500 μg/L. The results showed that pharmaceuticals have different influence on the amount of produced biogas even if they are from the same therapeutic group. In the low concentration, the inhibition was present for diclofenac, carbamazepine and amoxicillin, at the high concentration, while diclofenac showed almost no influence. Other compounds caused a stimulative effect on the process. The mixture of all pharmaceuticals of interest in low concentration was stimulative at first, while it was inhibotory since mid-time of the test.