Influence of surfactants on anaerobic digestion of waste activated sludge: acid and methane production and pollution removal

The objective of this study is to summarize the effects of surfactants on anaerobic digestion (AD) of waste activated sludge (WAS). The increasing amount of WAS has caused serious environmental problems. Anaerobic digestion, as the main treatment for WAS containing three stages (i.e. hydrolysis, acidogenesis, and methanogenesis), has been widely investigated. Surfactant addition has been demonstrated to improve the efficiency of AD. Surfactant, as an amphipathic substance, can enhance the efficiency of hydrolysis by separating large sludge and releasing the encapsulated hydrolase, providing more substance for subsequent acidogenesis. Afterwards, the short chain fatty acids (SCFAs), as the major product, have been produced. Previous investigations revealed that surfactant could affect the transformation of SCFA. They changed the types of acidification products by promoting changes in microbial activity and in the ratio of carbon to nitrogen (C/N), especially the ratio of acetic and propionic acid, which were applied for either the removal of nutrient or the production of polyhydroxyalkanoate (PHA). In addition, the activity of microorganisms can be affected by surfactant, which mainly leads to the activity changes of methanogens. Besides, the solubilization of surfactant will promote the solubility of contaminants in sludge, such as organic contaminants and heavy metals, by increasing the bioavailability or desorbing of the sludge.     

Effect of sulphidogenesis on acid-phase digestion of waste activated sludge

This paper reports the influence of sulfate-reducing bacterial activity on acidogenic digestion of waste activated sludge (WAS). A series of experiments was conducted by feeding WAS to a 10-l, completely mixed, mesophilic reactor maintained at pH 5.0 under sulfidogenic and non-sulfidogenic conditions. Analyses of volatile fatty acids indicated that the productions of acetic and propionic acids were slightly increased by sulfidogenic activity at 218 mg/l level of sulfate when COD sulfate ratio was 55:1. Higher amounts of methanol, ethanol and hydrogen were observed in the non-sulfidogenic condition, but ammonia was lower than in the moderate sulfidogenic runs. At 0.63 kg VS/m³ d loading rate the hydrolysis was above 90% in both moderate sulfidogenic and non- sulfidogenic runs. The results of these experiments showed the possible influence of moderate sulfidogenesis in the protein degradation of WAS anaerobic digestion. However, the acid-phase digestion was adversely affected by increasing the sulfate concentration to 400 mg/l.     

Thermophilic methane production from cattle waste

Methane production from waste of cattle fed a finishing diet was investigated, using four 3-liter-working volume anaerobic digestors at 60 degrees C. At 55 degrees C a start-up culture, in which waste was the only source of bacteria, was generated within 8 days and readily adapted to 60 degrees C, where efficiency of methanogenesis was greater. Increasing the temperature from 60 to 65 degrees C tended to drastically lower efficiency. When feed concentrations of volatile solids (VS, organic matter) were increased in steps of 2% after holding for 1 months at a given concentration, the maximum concentrations for efficient fermentation were 8.2, 10.0, 11.6, and 11.6% for the retention times (RT) of 3, 6, 9, and 12 days, respectively. The VS destructions for these and lower feed concentrations were 31 to 37, 36 to 40, 47 to 49 and 51 to 53% for the 3-, 6-, 9-, and 12-day RT digestors, respectively, and the corresponding methane production rates were about 0.16, 0.18, 0.20, and 0.22 liters/day per g of VS in the feed. Gas contained 52 to 57% methane. At the above RT and feed concentrations, alkalinity rose to 5,000 to 7,700 mg of CaCo3 per liter (pH to 7.5 to 7.8), NH3 plus NH4+ to 64 to 90 mM, and total volatile acids to 850 to 2,050 mg/liter as acetate. The 3-day RT digestor was quite stable up to 8.2% feed VS and at this feed concentration produced methane at the very high rate of 4.5 liters/day per liter of digestor. Increasing the percentage of feed VS beyond those values indicated above resulted in greatly decreased organic matter destruction and methane production, variable decrease in pH, and increased alkalinity, ammonia, and total volatile acid concentrations, with propionate being the first to accumulate in large amounts. In a second experiment with another lot of waste, the results were similar. These studies indicate that loading rates can be much higher than those previously thought useful for maximizing methanogenesis from cattle waste.     

Biogas production from anaerobic co-digestion of waste activated sludge: co-substrates and influencing parameters

Reviews in Environmental Science and Bio/Technology - Anaerobic digestion is a versatile biotechnology to treat waste activated sludge (WAS), the main by-products of biological wastewater...     

废弃活性污泥中产聚羟基脂肪酸酯菌株Bacillus sp. PB-3的发酵条件优化

通过尼罗红染色法结合荧光显微镜镜检,从废弃活性污泥中分离得到1株高产聚羟基脂肪酸酯(PHAs)的菌株Bacillus sp.PB-3,经气相色谱法鉴定该菌株胞内产物为聚β-羟基丁酸酯(PHB)。对培养基成分及发酵条件优化后,获得最佳培养方案:12 g/L的葡萄糖为C源,2 g/L的牛肉膏为N源,初始pH 7.5,培养基装液量80 mL,转速为200 r/min,37℃培养48 h,PHB质量分数可达菌体干质量的32.09%,比优化前提高30%。     

Thermophilic methane production from cattle waste.

Methane production from waste of cattle fed a finishing diet was investigated, using four 3-liter-working volume anaerobic digestors at 60 degrees C. At 55 degrees C a start-up culture, in which waste was the only source of bacteria, was generated within 8 days and readily adapted to 60 degrees C, where efficiency of methanogenesis was greater. Increasing the temperature from 60 to 65 degrees C tended to drastically lower efficiency. When feed concentrations of volatile solids (VS, organic matter) were increased in steps of 2% after holding for 1 months at a given concentration, the maximum concentrations for efficient fermentation were 8.2, 10.0, 11.6, and 11.6% for the retention times (RT) of 3, 6, 9, and 12 days, respectively. The VS destructions for these and lower feed concentrations were 31 to 37, 36 to 40, 47 to 49 and 51 to 53% for the 3-, 6-, 9-, and 12-day RT digestors, respectively, and the corresponding methane production rates were about 0.16, 0.18, 0.20, and 0.22 liters/day per g of VS in the feed. Gas contained 52 to 57% methane. At the above RT and feed concentrations, alkalinity rose to 5,000 to 7,700 mg of CaCo3 per liter (pH to 7.5 to 7.8), NH3 plus NH4+ to 64 to 90 mM, and total volatile acids to 850 to 2,050 mg/liter as acetate. The 3-day RT digestor was quite stable up to 8.2% feed VS and at this feed concentration produced methane at the very high rate of 4.5 liters/day per liter of digestor. Increasing the percentage of feed VS beyond those values indicated above resulted in greatly decreased organic matter destruction and methane production, variable decrease in pH, and increased alkalinity, ammonia, and total volatile acid concentrations, with propionate being the first to accumulate in large amounts. In a second experiment with another lot of waste, the results were similar. These studies indicate that loading rates can be much higher than those previously thought useful for maximizing methanogenesis from cattle waste.     

Response of activated sludge to the treatment of oxytetracycline production waste stream

To investigate how the microbial community in activated sludge responded to high antibiotic levels, a bench-scale aerobic wastewater treatment system was used to treat oxytetracycline (OTC) mother liquor (OTC-ML). Removal efficiency of chemical oxygen demand decreased from 64.9 to 51.0 % when the OTC level increased from 191.6 to 620.5 mg/L, respectively. According to the cloning results, Psychrobacter and Cryptophyta were the dominant bacterium and eukaryote in the inoculated sludge, respectively, both of which related to low temperature. After OTC exposure, Alphaproteobacteria and Betaproteobacteria became the dominant bacteria, with a small proportion of Firmicutes, Actinobacteria appeared, and fungi (mainly Saccharomycotina) became the dominant eukaryotes, indicating the possible functions of these microorganisms in the wastewater treatment of OTC-ML. The relative abundance of nine tetracycline resistance genes and four mobile elements (class 1 integron, class 2 integron, transposon Tn916/1545, and pattern 1 insertion sequence common region) significantly increased from undetectable to 2.1?×?10^?3 in the inoculated sludge to 1.7?×?10^?4–9.8?×?10^?1 in sludge exposed to 620.5 mg/L OTC by using real-time PCR. The variety of gene cassette arrays of class 1 integron in the sludge samples increased with increasing OTC exposure concentration.     

Parameters affecting protein production from brewery waste water in a multi-channel laboratory-scale activated sludge system

Summary With the aim of studying the possible utilization of brewery waste water activated sludge for animal feeding, the influence of the solids retention time (SRT) and nitrogen supplementation were investigated, especially with respect to biomass production and biomass composition. It was found that the SRT strongly influenced both parameters. At an SRT of from 4 to 6 days excellent biomass production was obtained. This biomass had the highest protein content and the daily protein production was four times higher than at a SRT of 20 days. Supplementation with urea doubled the protein production, lowered the carbohydrate and poly--hydroxybutyric acid content, but increased the nucleic acid content. The COD removal was better and phosphorus removal increased. In order to study these variables, a multi-channel laboratory system was designed. Because of its simplicity in operation and its versatility this system is described in detail.     

Effect of mixing duration and vacuum on methane production rate from beef cattle waste

The effects of mixing duration and vacuum on methane production rates from anaerobically fermented beef cattle wastes were discussed. The results showed that continuously mixed fermentors produced significantly (P < 0.05) higher methane production rates than fermentors mixed two hours per day. However, the rates from the continuously mixed fermentors were only 8-11% higher than the intermittently mixed fermentors at six and four days hydraulic retention time (HRT), respectively. There was no significant difference between the vacuum and conventional fermentors at six days HRT, but there was a significant difference at four days HRT. The CH(4) production rate of the vacuum fermentors was 5% higher than the conventional fermentors at four days HRT. The results of these experiments compared well with predicted CH(4) production rates. These results suggest that there is little potential for increasing the fermentation rates of livestock wastes by increased mixing or vacuum.     

添加厨余垃圾对剩余污泥厌氧消化产沼气过程的影响

为提高剩余污泥厌氧消化的沼气产量和甲烷含量,研究了厨余垃圾的不同添加量对剩余污泥厌氧消化性能的影响。结果表明,在35℃下,随着剩余污泥中厨余垃圾添加量的增加,厌氧消化系统中碳氮质量比（C／N）、胞外多聚物（EPS）等生理生化指标均有不同程度的改善。其中当剩余污泥与厨余垃圾质量比为2：1时,混合有机废弃物中沼气产量和甲烷含量均达到最大值,每克挥发性固体（VS）产生了156．56mL沼气,甲烷体积分数为67．52％,分别比剩余污泥单独厌氧消化时的产气量提高了5倍和1．5倍。     

Enhanced anaerobic gas production of waste activated sludge pretreated by pulse power technique

An electric pulse-power reactor consisting of one coaxial electrode and multiple ring electrodes was developed to solubilize waste activated sludge (WAS) prior to anaerobic digestion. By pretreatment of WAS, the soluble chemical oxygen demand (SCOD)/total chemical oxygen demand (TCOD) ratio and exocelluar polymers (ECP) content of WAS increased 4.5 times and 6.5 times, respectively. SEM images clearly showed that pulse-power pretreatment of WAS was found to result in destruction of sludge cells. Batch-anaerobic digestion of pulse-power treated sludge showed 2.5 times higher gas production than that of untreated sludge. Solubilized sludge cells by pulse-power pretreatment would be readily utilized for anaerobic microorganisms to produce anaerobically-digested gas. Slow or lagged gas production in the initial anaerobic digestion stage of pulse-power pretreated sludge implied that the methane-forming stage of anaerobic digestion would be the rate-limiting step for anaerobic digestion of pulse-power pretreated sludge.     

Strategy for minimization of excess sludge production from the activated sludge process

Increased attention has been given to minimization of sludge production from activated sludge process since environmental regulations are being more and more stringent in relation to excess sludge disposal. In a biological process, the more organic carbon utilized in carbon dioxide production, the fewer sludge produced, and vice versa. This paper, therefore, reviews strategies developed for minimization of excess sludge production, such as oxic-settling-anaerobic process, high dissolved oxygen process, uncoupler-containing activated sludge process, ozonation-combined activated sludge process, control of sludge retention time and biodegradation of sludge in membrane-assisted reactor. In these modified activated sludge processes, excess sludge production can be reduced by 20-100% without significant effect on process efficiency and stability. It is expected that this paper would be helpful for researchers and engineers to develop novel and efficient operation strategy to minimize sludge production from biological systems.     

Effect of nitrogen limitation on enrichment of activated sludge for PHA production

Polyhydroxyalkanoates (PHA) are good candidates to plastics because of their material properties similar to conventional plastics and complete biodegradability. The use of activated sludge can be a cheaper alternative to pure cultures for PHA production. In this study, effect of nitrogen limitation during acclimatization period of biomass on production of polyhydroxyalkanoate was investigated. Activated sludge was selected in two sequencing batch reactors operated with and without nitrogen limitation. Batch tests were performed to examine polymer productions of activated sludges acclimatized to different nitrogen regimes. Responses of biomass to different organic loading rates, organic acids, and carbon to nitrogen (C/N) ratios were studied by determining specific polymer storage rate, polymer storage yield, and sludge polymer content of biomasses. Results obtained from batch experiments showed that concentrations of polymer accumulated by two different sludges increased directly with initial substrate concentration. Observed highest polymer yields for the biomasses enriched with and without nitrogen deficiency were 0.69 g COD PHA g(-1) COD S and 0.51 g COD PHA g(-1) COD S, and corresponding polymer contents of biomasses were 43.3% (g COD PHA g(-1) COD X) and 38.3% (g COD PHA g(-1) COD X), respectively. Polymer yields for both biomasses decreased with substrate shift however, biomass enriched with nitrogen deficiency adapted well to acetate-propionate mixture. The results presented in this study showed that polymer storage ability of biomass was improved more under dynamic conditions with nitrogen deficiency when compared to that without nitrogen deficiency. Limiting ammonia availability during batch experiments also caused higher polymer production by suppressing growth, as well as during enrichment of biomass.     

New sludge pretreatment method to improve dewaterability of waste activated sludge

The enhancements of electrolysis-pretreated conditioning were investigated in this study. Normalized capillary suction time (CST) was used to evaluate sludge dewaterability. Extracellular polymeric substance (EPS) concentration, viscosity and scanning electron microscopy (SEM) were determined to explain the observed changes in conditioning process. It indicated that pretreatment at 50 v and 5 min with Ti/RuO₂ anode was determined to be the optimal condition, which generated the lowest normalized CST and optimal soluble EPS concentration, leading to the decreasing of viscosity. EPS had positive correlation with the normalized CST. Subjecting to a combination of electrolysis pretreatment and flocculants conditioning, 50% dosage of cationic polyacrylamide (PAM) could be reduced. When co-conditioned with electrolysis and polymerization ferric sulfate (PFS), it did not present any clear advantages over PFS conditioning alone. Furthermore, SEM investigation indicated that electrolysis pretreatment could rupture sludge, release the interstitial water and extracellular substances, especially protein and polysaccharide, and consequently enhance its dewaterability.     

Dewaterability of waste activated sludge with ultrasound conditioning

This study investigated the potential benefits of ultrasound-conditioned sludge dewatering treatments with specific energy dosages from 0 to 35,000 kJ/kg total solids (TS). Capillary suction time (CST) and specific resistance of filtration (SRF) were used to evaluate sludge dewaterability. Sludge water distribution was measured by the drying test and mechanical separation methods. Both extracellular polymeric substance (EPS) content and sludge particle size were determined in an attempt to explain the observed changes in sludge dewaterability. The results indicated that application of low specific energy dosages (<4400 kJ/kg TS) slightly enhanced sludge dewaterability, but larger specific energy dosages (>4400 kJ/kg TS) significantly deteriorated sludge dewaterability. The optimal specific energy to give maximal dewaterability characteristics was found to be 800 kJ/kg TS, which generated sludge with optimal EPS concentration (400-500 mg/l) and particle size distribution (80-90 microm diameter). Subjecting sludge to a combination of cationic polymer and ultrasound pretreatments did not present any clear advantages over polymeric conditioning alone for improving sludge dewaterability. The effects of cationic polymer treatment predominated over those of ultrasound pretreatment when both were used together.     

PHA production by activated sludge.

The production of polyhydroxyalkanoate by anaerobic-aerobic activated sludge was reviewed concentrating on the biochemical mechanisms and on the trials to increase polyhydroxyalkanoate (PHA) content in activated sludge. The anaerobic aerobic activated sludge system selects microorganisms with the capabilities to couple glycolysis, polyphosphate degradation, and PHA accumulation for anaerobic substrate uptake. Some of the PHA-related metabolisms observed there have not been seen in pure cultures so far. Such metabolisms are the formation of PHA containing 3-hydroxy-2-methylvalerate, and '3-hydroxyvalerate fermentation' in which glucose or glycogen is converted to 3-hydroxyvalerate-rich PHA while yielding energy. The PHA content of activated sludge can be increased up to 62% by applying a microaerophilic-aerobic activated sludge process. PHA production by activated sludge is worth investigation.     

Effects and model of alkaline waste activated sludge treatment

Due to lack of information about alkaline sludge treatment with high dose at ambient temperature, alkaline sludge treatment was investigated to know the effects of different doses (0-0.5 mol/L) of sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)2] at 0-40 degrees C. Results showed that NaOH was more suitable than Ca(OH)2 for sludge disintegration. For NaOH treatment, most efficient dose was about 0.05 mol/L (0.16 g/g dry solid), and 60-71% solubilization of organic matters was achieved in first 30 min during its treatment of 24h. The process is described by a transmutative power function model, and relation between reaction rate constant and temperature are according with Arrhenius equation. Low dose NaOH treatment (<0.2 mol/L) deteriorated sludge dewatering ability obviously, while the ability was recovered gradually with the increase of NaOH dose. For Ca(OH)2 treatment, the disintegrated floc fragments and soluble organic polymers can be re-flocculated with the help of calcium cations. Consequently sludge disintegration effect was counteracted and dewatering ability improved.