Waste Activated Sludge Alkaline Fermentation Research Articles

Revealing the Mechanism of Biochar Enhancing the Production of Medium Chain Fatty Acids from Waste Activated Sludge Alkaline Fermentation Liquor

In this work, the effectiveness of biochar with distinctively different particle sizes (i.e., 2000–5000 and 75–150 μm) derived from anaerobically digested sludge was comprehensively evaluated in the production of enhancing MCFAs (medium chain fatty acids) using waste activated sludge alkaline fermentation liquor as feedstock with ethanol as the electron donor. The results showed that fine biochar (i.e., 75–150 μm) was more favorable for enhancing the production of MCFAs with an increased electron transfer efficiency reaching 92.6%. Metagenomic analysis revealed that the total microbial taxonomic composition shifted in favor of the production of MCFAs (e.g., Clostridium kluyveri sp., Clostridium magnum sp., and Clostridium botulinum sp.). The increased relative abundance of functional enzymes associated with the production of MCFAs confirmed that both the reverse β-oxidation pathway and the fatty acid biosynthesis pathway were enhanced by biochar. Mechanistic studies revealed that the biochar had high redox-active properties due to the functional groups (mainly quinones and hydroquinone) on its surface and an important ability to charge and/or discharge, which thus promoted the transfer of electrons for the production of MCFAs during the CE process.

Medium-Chain fatty acids and long-chain alcohols production from waste activated sludge via two-stage anaerobic fermentation

Traditional bioenergy recovery in the form of short chain fatty acids (SCFAs) from waste activated sludge (WAS) is generally limited by economic unattractiveness and complexity of products separation. Herein, a novel biotechnology process of two-stage anaerobic fermentation for converting the WAS into high energy density, easy-separated medium chain fatty acids (MCFAs) and long-chain alcohols (LCAs) was evaluated. In this process, the WAS was first converted to WAS alkaline fermentation liquid (WASAFL), serving as electron acceptors (EAs) and inoculum, then adding ethanol as electron donor (ED) for chain elongation (CE). The co-production of MCFAs and LCAs during CE were studied under three different ED to EA ratios, i.e., 3:1, 4:1 and 5:1. Experimental results demonstrated that when the ratio of ED to EA increased from 3:1 to 5:1, the production of MCFA and LCAs respectively increased from 5.57 ± 0.17 and 2.58 ± 0.18 to7.67 ± 0.48 and 4.21 ± 0.19 g COD/L. A similar observation was made in the total product electron efficiency, increasing from 59.9% to 72.1%. However, the highest total product selectivity (i.e., 68.0%) and highest products production yield (i.e., 59.77%) were not achieved at the ED to EA ratio of 5:1 due to toxicity caused by higher accumulation of n-caproate. The kinetic analysis further confirmed that high ratio of ED to EA induced improvement in product maximum yield, production rate for both MCFAs and LCAs. Microbial community analysis indicated that Clostridium, Caproiciproducens, Acinetobacter, Exilispira, and Oscillibacter were clearly enriched in the CE reactor and had positive correlation with MCFAs and LCAs production.

Effect of Salinity on Enhancing Waste Activated Sludge Alkaline Fermentation at Different Temperatures

Clean – Soil, Air, Water 2016, 44, 1750–1758 https://doi.org/10.1002/clen.201500351 The printed version of the article contains an error in the affiliation of one of the co-authors, Baikun Li: Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Engineering Research Center of Beijing, Beijing University of Technology, Beijing 100124, China The correct affiliation should be the following: Baikun Li, Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269, United States The authors would like to apologize for any inconvenience caused.

Three birds with one stone: Lower volatile fatty acids (VFAs) reduction, higher phosphorus (P) removal, and lower alkali consumption via magnesium dosing after waste activated sludge (WAS) alkaline fermentation

Magnesium (120 mmol/L) was dosed to investigate the effects of different methods and times on performance of waste activated sludge (WAS) alkaline fermentation. The investigation revealed that maximum soluble chemical oxygen demand (SCOD) was achieved without magnesium addition, indicating magnesium addition, regardless of dosing method or time, could constrain the sludge hydrolysis process. Fermented sludge dewaterability was improved with magnesium addition, as based on results of capillary suction time (CST) and bound water. The optimal magnesium dosage was reached following WAS alkaline fermentation, in which little volatile fatty acids (VFAs) reduction (67 mg COD/L), higher PO43--P removal efficiency (95.41%), and lower alkali consumption were achieved. Further, 682.19 mg chemical oxygen demand (COD)/L of the released protein was precipitated, suggesting that soluble protein was effectively recovered from sludge with magnesium addition after fermentation. In conclusion, dosing magnesium after WAS alkaline fermentation has multiple merits and warrants further study.

In-situ ammonia stripping with alkaline fermentation of waste activated sludge to improve short-chain fatty acids production and carbon source availability

Alkaline fermentation of waste activated sludge (WAS) to produce short-chain fatty acids (SCFAs) has been proved to be promising to develop internal carbon source for denitrifying processes in municipal wastewater treatment plants. However, a large amount of ammoniacal nitrogen also releases during fermentation, resulting in inhibition of acidogenic process and reduction of carbon source availability. Alkaline fermentation of WAS combined with in-situ ammonia stripping was proposed to improve SCFAs production and carbon source availability simultaneously. The results showed that a maximal SCFAs production of 308.7 ± 4.8 mg chemical oxygen demand/g volatile suspended solid was achieved under the pH = 10 + In-situ ammonia stripping, which was 21.7% and 141.5% higher than that of the pH = 10 and the control, respectively. Most of the ammoniacal nitrogen was stripped out, and the WAS-derived SCFAs availability as carbon source increased by 103.2%. These findings indicate in-situ ammonia stripping could make alkaline fermentation of WAS more practical.

Unveiling the mechanisms of medium-chain fatty acid production from waste activated sludge alkaline fermentation liquor through physiological, thermodynamic and metagenomic investigations

Effective sludge treatment with bioenergy production is attracting increasing interests as large quantities of waste activated sludge (WAS) are produced during the wastewater treatment. In this study, a new biotechnical process for converting the WAS alkaline fermentation liquor (WASAFL) into valuable, easy-separated medium chain fatty acids (MCFAs) through chain elongation (CE) was investigated, which may provide a new insight into sludge treatment. In the process, ethanol was served as the electron donor (EDs) and WASAFL were main electron acceptors (EAs). The MCFAs productions were investigated under three different ED to EA ratios (i.e., 1:2, 1:1 and 2:1). The result showed that MCFAs production was increased from 2.88 ± 0.01 to 5.28 ± 0.18 g COD/L with the increase of ED to EA ratio. However, the highest MCFA selectivity was achieved at 72.9% when the ED to EA ratio was 1:1. The decrease in the selectivity at high ED:EA ratio is mainly due to the production of higher alcohol (i.e., n-butanol and n-hexanol). The thermodynamic analysis confirmed all CE processes for MCFAs production from WASAFL were exothermic reactions, with the spontaneity and energy release of the reactions increased with the ethanol level. The microbial community analysis showed that the relative abundances of Clostridium, Oscillibacter, Leptolinea and Exilispira were positively correlated with the MCFAs production. The metagenomic analysis suggested that both the reverse β-oxidization pathway and fatty acid biosynthesis pathway contributed to the CE process in the studied system. The functional enzymes were mainly associated within Clostridium, with Clostridium Kluyveri, Clostridium botulinum and Clostridium magnum being likely the key species responsible for the CE process.

The role of a newly isolated strain Corynebacterium pollutisoli SPH6 in waste activated sludge alkaline fermentation.

Alkaline fermentation has been considered as one of the efficient methods for waste activated sludge (WAS) treatment, but usually limited by microbial fermentation activities under extreme pH condition. One newly isolated alkali-tolerant strain Corynebacterium pollutisoli SPH6 was used to assess its potential role and effect on WAS alkaline fermentation process. Results from response surface method showed that the optimal organic nitrogen degradation rate by SPH6 was obtained under temperature of 35 °C, initial pH of 10, shaking speed of 80 rpm, inoculation ratio of 6.5%. Batch-scale experiments demonstrated that, compared with the control group, the inoculation of SPH6 finally achieved higher productions with 13.4% of carbohydrates, 27.1% of protein and 25.4% of total volatile fatty acids (VFAs), and more predominant functional bacteria characterized by high-throughput sequencing, such as genera Acinetobacter in phylum Proteobacteria, Tissierella and Acetoanaerobium in phylum Firmicutes. The strain SPH6 might play a vital role in maintaining and facilitating the growth and diversity of functional bacteria in WAS alkaline fermentation process. It has implied promising practical application of the present strain in enhancing WAS reduction and utilization.

Alkaline fermentation of waste activated sludge with calcium hydroxide to improve short-chain fatty acids production and extraction efficiency via layered double hydroxides

Ca(OH)2 addition was proposed to improve short chain fatty acids (SCFAs) production via alkaline fermentation of waste activated sludge (WAS), with CO32− and PO43− being removed simultaneously, so that the SCFAs extraction efficiency could be improved. Alkaline fermentation of WAS with Ca(OH)2 and NaOH addition were performed respectively, and the efficiencies of SCFAs extraction from the fermentation liquids via in situ layered double hydroxides (LDHs) were investigated. The results showed that, the SCFAs production was much more improved with NaOH addition than that with Ca(OH)2 addition. However, the SCFAs contents in the synthesized SCFAs-LDH were 6.7 ± 0.4 mg COD/L (control), 12.4 ± 0.5 mg COD/L (with NaOH addition) and 17.4 ± 0.4 mg COD/L (with Ca(OH)2 addition), respectively. This means that Ca(OH)2 addition is an effective way to improve SCFAs extraction from fermentation liquid of WAS.

A novel process for volatile fatty acids production from syngas by integrating with mesophilic alkaline fermentation of waste activated sludge

The present study proposed and demonstrated a novel process for the bioconversion of syngas (mainly CO and H2) to valuable volatile fatty acids (VFA) by integrating with mesophilic alkaline fermentation of waste activated sludge (WAS). The results showed that although pH 9 was suitable for VFA production from WAS, 62.5% of the consumed CO was converted to methane due to the presence of hydrogenogenic pathway for CO conversion. The increase of pH from 9 to 9.5 inhibited the methane production from CO because of the possible presence of only acetogenic pathway for CO conversion. However, methane was still produced from H2 contained in syngas through hydrogenotrophic methanogenesis, and around 32–34% of the consumed syngas was converted to methane. At both pH 9 and 9.5, methane was produced by hydrogenotrophic methanogens Methanobacteriales. Further increase of pH to 10 effectively inhibited methane production from syngas, and efficient VFA (mainly acetate with the concentration of around 135 mM) production by simultaneous conversion of syngas and WAS was achieved. High acetate concentrations (>150 mM) were shown to have serious negative effects on the conversion of syngas. The addition of syngas to the mesophilic alkaline fermentation of WAS at pH 10 not only resulted in the enrichment of some known bacteria related with syngas conversion, but also changed the microbial community compositions for the fermentation of WAS.

Effect of Salinity on Enhancing Waste Activated Sludge Alkaline Fermentation at Different Temperatures

Carbon source shortage and waste sludge treatment are two problems facing sewage treatment plants. The purpose of this work was to investigate the feasibility of using salt (NaCl) to enhance the production of short‐chain fatty acids (SCFAs) from waste sludge, reduce sludge production, and lower the operating cost. Four sodium chloride (NaCl) concentrations (0, 2, 15, and 25 g/L) and temperatures (20, 30, 35, and 40°C) were examined individually in batch‐mode sludge fermentation systems. The results showed that NaCl promoted the release of soluble proteins and polysaccharides, enhanced hydrolysis acidification and SCFAs accumulation, suppressed the activity of coenzyme 420 and the growth of methanogens. The optimal condition of hydrolysis acidification was 15 g/L NaCl and 35°C, and the acidification was deteriorated at 25 g/L NaCl and 40°C. Compared with the blank test (0 g/L NaCl), the sludge reduction and SCFAs production increased by 22.12 and 21.21%, respectively. With regard to the alkali consumption per unit (1 mmol), the SCFAs production and sludge reduction was increased by 9.6 and 21.99%.

Pilot-Scale Waste Activated Sludge Alkaline Fermentation, Fermentation Liquid Separation, and Application of Fermentation Liquid To Improve Biological Nutrient Removal

The use of sludge fermentative short-chain fatty acids (SCFA) as an additional carbon source of biological nutrient removal (BNR) has drawn much attention recently as it can reuse sludge organics, reduce waste activated sludge production, and improve BNR performance. Our previous laboratory study had shown that the SCFA production was significantly enhanced by controlling sludge fermentation at pH 10 with NaOH. This paper focused on a pilot-scale study of alkaline fermentation of waste activated sludge, separation of the fermentation liquid from the alkaline fermentation system, and application of the fermentation liquid to improve municipal biological nitrogen and phosphorus removal. NaOH and Ca(OH)(2) were used respectively to adjust the alkaline fermentation pH, and their effects on sludge fermentation and fermentation liquid separation were compared. The results showed that the use of Ca(OH)(2) had almost the same effect on SCFA production improvement and sludge volatile suspended solids reduction as that of NaOH, but it exhibited better sludge dewatering, lower chemical costs, and higher fermentation liquid recovery efficiency. When the fermentation liquids, adjusted with Ca(OH)(2) and NaOH respectively, were added continuously to an anaerobic-anoxic-aerobic municipal wastewater BNR system, both the nitrogen and phosphorus removals, compared with the control, were improved to the same levels. This was attributed to the increase of not only influent COD but also denitrifying phosphorus removal capability. It seems that the use of Ca(OH)(2) to control sludge fermentation at pH 10 for efficiently producing a carbon source for BNR is feasible.

Understanding Short-Chain Fatty Acids Accumulation Enhanced in Waste Activated Sludge Alkaline Fermentation: Kinetics and Microbiology

Most of the studies on sewage sludge treatment in literature were conducted for methane generation under acidic or near neutral pH conditions. It was reported in our previous studies that the accumulation of short-chain fatty acids (SCFAs), the preferred carbon source of biological wastewater nutrient removal, was significantly enhanced when sludge was fermented under alkaline conditions, but the optimal pH was temperature-dependent (pH 10 at ambient temperature, pH 9 at mesophilic, and pH 8 at thermophilic), and the maximal SCFAs yields were in the following order: thermophilic pH 8 > mesophilic pH 9 > ambient pH 10 > ambient uncontrolled pH. In this study the kinetic and microbiological features of waste activated sludge fermented in the range of pH 7-10 were investigated to understand the mechanism of remarkably high SCFAs accumulation under alkaline conditions. The developed sludge alkaline fermentation model could be applied to predicate the experimental data in either batch or semicontinuous sludge alkaline fermentation tests, and the relationships among alkaline pH, kinetic parameters, and SCFAs were discussed. Further analyses with fluorescence in situ hybridization (FISH) and PCR-based 16S rRNA gene clone library indicated that both the ratio of bacteria to archaea and the fraction of SCFAs producer accounting for bacteria were in the sequence of thermophilic pH 8 > mesophilic pH 9 > ambient pH 10 > ambient uncontrolled pH, which was in correspondence with the observed order of maximal SCFAs yields.

Using Sludge Fermentation Liquid To Improve Wastewater Short-Cut Nitrification-Denitrification and Denitrifying Phosphorus Removal via Nitrite

Wastewater biological nutrient removal (BNR) by short-cut nitrification-denitrification (SCND) and denitrifying phosphorus removal via nitrite (DPRN) has several advantages, such as organic carbon source saving. In this paper, a new method, i.e., by using waste activated sludge alkaline fermentation liquid as BNR carbon source, for simultaneously improving SCND and DPRN was reported. First, the performance of SCND and DPRN with sludge fermentation liquid as carbon source was compared with acetic acid, which was commonly used in literatures. Sludge fermentation liquid showed much higher nitrite accumulation during aerobic nitrification than acetic acid (81.8% versus 40.9%), and the former had significant anoxic denitrification and phosphorus uptake. The soluble phosphorus and total nitrogen removal efficiencies with sludge fermentation liquid were much higher than with acetic acid (97.6% against 73.4% and 98.7% versus 79.2%). Then the mechanisms for sludge fermentation liquid showed higher SCND and DPRN than acetic acid were investigated from the aspects of wastewater composition, microorganisms assayed by 16S rRNA gene clone library, and fluorescence in situ hybridization. More NO(2)(-)-N accumulated by the use of sludge fermentation liquid was attributed to be more humic acids in the influent, which inhibited nitrite oxidizing bacteria (NOB) more serious than ammonia oxidizing bacteria (AOB), and more AOB but less NOB were observed in the BNR system. The reasons for sludge fermentation liquid BNR system exhibiting greater short-cut denitrifying phosphorus removal were that there were less glycogen accumulating organisms and more phosphorus accumulating organisms and anoxic denitrifying phosphorus removal bacteria with higher nitrite reductase activity.

Waste Activated Sludge Alkaline Fermentation Liquid as Carbon Source for Biological Nutrients Removal in Anaerobic Followed by Alternating Aerobic-Anoxic Sequencing Batch Reactors

Activated sludge process has been widely used to remove phosphorus and nitrogen from wastewater. However, the nitrogen and phosphorus removal is sometimes unsatisfactory due to the low influent COD. Another problem with the activated sludge process is that large amount of waste activated sludge is produced, which needs further treatment. In this study, the waste activated sludge alkaline fermentation liquid was used as the main carbon source for phosphorus and nitrogen removal under anaerobic followed by alternating aerobic-anoxic conditions, and the results were compared with those using acetic acid as the carbon source. The use of alkaline fermentation liquid not only affected the transformations of phosphorus, nitrogen, intracellular polyhydroxyalkanoates and glycogen, but also led to higher removal efficiencies for phosphorus and nitrogen compared with acetic acid. It was observed that ammonium was completely removed with either alkaline fermentation liquid or acetic acid as the carbon source. However, the former resulted in higher removal efficiencies for phosphorus (95%) and nitrogen (82%), while the latter showed lower ones (87% and 74%, respectively). The presence of a large amount of propionic acid in the alkaline fermentation liquid was one possible reason for its higher phosphorus removal efficiency. Exogenous instead of endogenous denitrification was the main pathway for nitrogen removal with the alkaline fermentation liquid as the carbon source, which was responsible for its higher nitrogen removal efficiency. It seems that the alkaline fermentation liquid can replace acetic acid as the carbon source for phosphorus and nitrogen removal in anaerobic followed by alternating aerobic-anoxic sequencing batch reactor.

Recovery of nitrogen and phosphorus from alkaline fermentation liquid of waste activated sludge and application of the fermentation liquid to promote biological municipal wastewater treatment

In previous publications we reported that by controlling the pH at 10.0 the accumulation of short-chain fatty acids (SCFA) during waste activated sludge (WAS) fermentation was remarkably improved [Yuan, H., Chen, Y., Zhang, H., Jiang, S., Zhou, Q., Gu, G., 2006. Improved bioproduction of short-chain fatty acids (SCFAs) from excess sludge under alkaline conditions. Environ. Sci. Technol. 40, 2025–2029], but significant ammonium nitrogen (NH 4–N) and soluble ortho-phosphorus (SOP) were released [Chen, Y., Jiang, S., Yuan, H., Zhou, Q., Gu, G., 2007. Hydrolysis and acidification of waste activated sludge at different pHs. Water Res. 41, 683–689]. This paper investigated the simultaneous recovery of NH 4–N and SOP from WAS alkaline fermentation liquid and the application of the fermentation liquid as an additional carbon source for municipal wastewater biological nitrogen and phosphorus removal. The central composite design (CCD) of the response surface methodology (RSM) was employed to optimize and model the simultaneous NH 4–N and SOP recovery from WAS alkaline fermentation liquid. Under the optimum conditions, the predicted and experimental recovery efficiency was respectively 73.4 and 75.7% with NH 4–N, and 82.0 and 83.2% with SOP, which suggested that the developed models described the experiments well. After NH 4–N and SOP recovery, the alkaline fermentation liquid was added to municipal wastewater, and the influence of volume ratio of fermentation liquid to municipal wastewater (FL/MW) on biological nitrogen and phosphorus removal was investigated. The addition of fermentation liquid didn't significantly affect nitrification. Both SOP and total nitrogen (TN) removal were increased with fermentation liquid, but there was no significant increase at FL/MW greater than 1/35. Compared to the blank test, the removal efficiency of SOP and TN at FL/MW = 1/35 was improved from 44.0 to 92.9%, and 63.3 to 83.2%, respectively. The enhancement of phosphorus and nitrogen removal was mainly attributed to the increase of influent SCFA, or rather, the increase of intracellular polyhydroxyalkanoates (PHA) which served as the carbon and energy sources for denitrification and phosphorus uptake. The addition of alkaline fermentation liquid to municipal wastewater, however, increased the effluent COD, which was caused mainly by the increase of influent humic acid, not protein or carbohydrate.

Enhanced Biological Phosphorus Removal Driven by Short-Chain Fatty Acids Produced from Waste Activated Sludge Alkaline Fermentation

This paper examines the feasibility of using alkaline fermentative short-chain fatty acids (SCFAs) as the carbon sources of enhanced biological phosphorus removal (EBPR) microorganisms. First, the released phosphorus was recovered from the SCFA-containing alkaline fermentation liquid by the formation of struvite precipitation, and 92.8% of the soluble ortho-phosphorus (SOP) could be recovered under conditions of Mg/P = 1.8 (mol/mol), pH 10.0, and a reaction time of 2 min. One reason for a Mg addition required in this study that was higher than the theoretical value was thatthe organic compounds consumed Mg. Then, two sequencing batch reactors (SBRs) were operated, respectively, with acetic acid and alkaline fermentative SCFAs as the carbon source of EBPR. The transformations of SOP, polyhydroxyalkanoates (PHAs), and glycogen and the removal of phosphorus were compared between two SBRs. It was observed that the phosphorus removal efficiency was around 98% with the fermentative SCFAs, and about 71% with acetic acid, although the former showed much lower transformations of both PHAs and glycogen. The reasons that fermentative SCFAs caused much higher SOP removal than acetic acid were due to less PHAs used for glycogen synthesis and a higher PHA utilization efficiency for SOP uptake. Finally, the toxicity of fermentation liquid to EBPR microorganisms was examined, and no inhibitory effect was observed. It can be concluded from this studythatthe SCFAs from alkaline fermentation of waste activated sludge were a superior carbon source for EBPR microorganisms than pure acetic acid.