Effects of Potassium Ferrate and Low-Temperature Thermal Hydrolysis Co-Pretreatment on the Hydrolysis and Anaerobic Digestion Process of Waste Activated Sludge

This study evaluated the effect of potassium ferrate(PF)and low-temperature thermal hydrolysis co-pretreatment on the promotion of sludge hydrolysis process and the impact on acid production in the subsequent anaerobic digestion process.The analytical investigations showed that co-pretreatment significantly facilitated the hydrolysis process of the sludge and contributed to the accumulation of short-chain fatty acids(SCFAs).The pretreatment conditions under the optimal leaching of organic matter from sludge were hydrothermal temperature of 75℃,hydrothermal treatment time of 12 h,and PF dosage of 0.25 g g^(−1)TSS(total suspended solids),according to the results of orthogonal experiments.By pretreatment under proper conditions,the removal rate of soluble chemical oxygen demand(SCOD)achieved 71.8%at the end of fermentation and the removal rate of total phosphorus(TP)was 69.1%.The maximum yield of SCFAs was 750.3 mg L^(−1),7.45 times greater than that of the blank group.Based on the analysis of the anaerobic digestion mechanism,it was indicated that the co-pretreatment could destroy the floc structure on the sludge surface and improve organic matter dissolving,resulting in more soluble organic substances for the acidification process.Furthermore,microbial community research revealed that the main cause of enhanced SCFAs generation was an increase in acidogenic bacteria and a reduction of methanogenic bacteria.

Effects of ultrasonic pretreatment on sludge dewaterability and extracellular polymeric substances distribution in mesophilic anaerobic digestion

Effect of ultrasonic pretreatment on sludge dewaterability was determined and the fate of extracellular polymeric substances （EPS） matrix in mesophilic anaerobic digestion after ultrasonic pretreatment was studied. Characteristics of proteins （PN）, polysaccharides （PS）, excitation-emission matrix （EEM） fluorescence spectroscopy and molecular weight （MW） distribution of dissolved organic matters （DOM） in different EPS fractions were evaluated. The results showed that after ultrasonic pretreatment, the normalized capillary suction time （CST） decreased from 44.4 to 11.1 （sec·L）/g total suspended solids （TSS） during anaerobic digestion, indicating that sludge dewaterability was greatly improved. The normalized CST was significantly correlated with PN concentration （R2 = 0.92, p 〈 0.01） and the PN/PS ratio （R2 = 0.84, p 〈 0.01） in the loosely bound EPS （LB-EPS） fraction. Meanwhile, the average MW of DOM in the LB- EPS and tightly bound EPS （TB-EPS） fractions also had a good correlation with the normalized CST （R2 〉 0.66, p 〈 0.01）. According to EEM fluorescence spectroscopy, tryptophan-like substances intensities in the slime, LB-EPS and TB-EPS fractions were correlated with the normalized CST. The organic matters in the EPS matrix played an important role in influencing sludge dewaterability.

Analysis on Present Situation of Anaerobic Digestion Products of Sludge in Landscaping Application and Market Demand in Chongqing

Taking the anaerobic digestion products of sludge as the object, through the analysis on the development of garden substrate market at home and abroad and the development status of horticultural products from the anaerobic digestion products, the direction for the utilization of the anaerobic digestion products of sludge was pointed out. Based on the demand of Chongqing’s garden market, this paper analyzed the potential utilization of sludge anaerobic digestion products in Chongqing, and briefly introduced the research status of landscaping utilization of sludge anaerobic digestion products in Chongqing, in order to provide reference for the industry.

Effect of Sludge from Different Sources on Solid Anaerobic Digestion of Corn Straw

[Objective] The aim was to study on effect of sludge from different sources on biogas yield efficiency through anaerobic digestion of corn straw. [Method] The present research studied on daily biogas yield and the accumulated biogas amount through anaerobic digestion of corn straw and sludges from four sources. [Result] The accumulated biogas yields produced from sludges in four sources from high to low were granular sludge, river sediments, concentrated sludge and filtered sludge. The first one proved the highest at 3.73 and 56.29 L/kg VS in daily biogas yield and the accumulated biogas. [Conclusion] The research laid foundation for full utilization of straw, improvement of energy utilization and sustainable development.

Bioelectricity from Anaerobic Co-Digestion of Organic Solid Wastes and Sewage Sludge Using Microbial Fuel Cells (MFCs)

Recently microbial fuel cells (MFCs) have been considered as an alternative power generation technique by utilizing organic wastes. In this study, an experiment was carried out to generate bioelectricity from co-digestion of organic waste (kitchen waste) and sewage sludge as a waste management option using microbial fuel cell (MFC) in anaerobic process. A total of five samples with different sludge-waste ratio were used with zinc (Zn) and cupper (Cu) as cell electrodes for the test. The trends of voltage generation were different for each sample in cells such as 350 mV, 263 mV, 416 mV maximum voltage were measured from sample I, II and III respectively. It was observed that the MFC with sewage sludge showed the higher values (around 960 mV) of voltages with time whereas 918 mV obtained with organic waste. Precisely comparing cases with varying the organic waste and sewage sludge ratio helps to find the best bioelectricity generation option. Using MFCs can be appeared as the solution of electricity scarcity along the world as an efficient and eco-friendly manner as well as organic solid waste and sewage sludge management.

Bioenergy Production from Anaerobic Co-Digestion of Sewage Sludge and Abattoir Wastes

Energy is the pillar of human economic development. Several energy sources, renewable and non-renewable, have been exploited to assure and sustain the need for sustainable development. However, depletion of non-renewable energy sources forced researchers to search for alternative cost effective and environmental friendly energy sources. Thus, conversion of waste materials into energy has obtained considerable attention. In line with this, the aim of this study is to investigate the improvement of bio-energy production through anaerobic digestion of mixture of wastes from sewage sludge and abattoir sources. The abattoir waste is functioned as a co-substrate. Laboratory scale batch anaerobic co-digestion of the waste is carried out under mesophilic condition for 20 days. Sewage Sludge (SS) alone, and different mix ratios of SS to Abattoir Waste (AW) were analyzed for bioenergy production. Besides, the nutrient values and reduction in volume of the sewage after digestion were determined. The results show that methane productions of 33.8%, 48.3% and 56.9% were obtained for SS alone and for SS:AW mix ratios of 4:1 and 3:2, respectively. The nutrient values of the slurry increased as mix ratio decreased due to the increase in the amount of AW. The obtained results indicate that bio-energy production can be improved through co-digestion of SS using AW as a co-substrate;thus warranting further investigation for the practical application in the energy production.

Effects of inoculating microorganisms on mesophilic anaerobic digestion of septic sludge

The anaerobic digestion of septic sludge was studied through inoculating effective microorganisms (EMs) under mesophilic condition (35 ℃). The variation of COD,total solid (TS),volatile solid (VS),pH value and the gas production rate during the digestion process were presented,and the optimal adding concentration of EMs was determined by comparing the reduction effectiveness of septic sludge. The results show that proper addition of EMs can enhance acid buffering capacity of the system,and the NH3-N concentration is lower than inhibition concentration of 2 g/L reported in the literature and maintain the range of pH value which is suitable for both hydrolysis-acidification and methanogenesis. However,overdose of EMs can reduce the initial pH value of septic sludge and decrease the effects of the anaerobic digestion. EMs can increase the quantity of microbe in septic sludge and improve the gas production and generation rate over a period of time. But overdosing EMs can lead to low pH,restrain activity of methanogenic bacteria and affect the quantity and the generation rate of gas. Adding 0.01% EMs achieves the highest sludge reduction with the removal rates of TS,VS and COD by 32.51%,42.34% and 40.97%,respectively.

Experimental Study on Anaerobic Digestion of Remaining Sludge in Municipal Wastewater Treatment Plant

Along with the development and progress of environmental protection management,it is necessary to pay full attention to the disposal of excess sludge in the process of urban sewage treatment plant management.It is necessary to ensure effective integration of management mechanisms and management paths.To a certain extent,it can improve the actual efficiency of digestion and treatment work and lay a foundation for the optimal operation of environmental protection management.In this paper,the treatment of excess sludge in a sewage treatment plant is studied.The method and results of anaerobic digestion test of excess sludge in a sewage treatment plant are discussed for reference only.

Ultrasonication as anaerobic digestion pretreatment to improve sewage sludge methane production:Performance and microbial characterization

A large amount of sludge is inevitably produced during sewage treatment.Ultrasonication(US)as anaerobic digestion(AD)pretreatment was implemented on different sludges and its effects on batch and semi-continuous AD performance were investigated.US was ef-fective in sludge SCOD increase,size decrease,and CH_(4)production in the subsequent AD,and these effects were enhanced with an elevated specific energy input.As indicated by semi-continuous AD experiments,the mean daily CH_(4)production of US-pretreated A^(2)O-,A^(2)O-MBR-,and AO-AO-sludgewere 176.9,119.8,and 141.7 NmL/g-VSadded,whichwere 35.1%,32.1%and 78.2%higher than methane production of their respective raw sludge.The US of A^(2)O-sludge achieved preferable US effects and CH_(4)production due to its high organic con-tent andweak sludge structure stability.In response to US-pretreated sludge,amore diverse microbial community was observed in AD.The US-AD system showed negative net energy;however,it exhibited other positive effects,e.g.,lower required sludge retention time and less residual total solids for disposal.US is a feasible option prior to AD to improve anaer-obic bioconversion and CH_(4)yield although further studies are necessary to advance it in practice.

Performance evaluation of up-flow anaerobic sludge blanket(UASB) reactor for treatment of paper mill wastewater

The present study deals with the performance evaluation of the UASB reactor under varied organic loading rate(OLR) for the treatment of paper mill wastewater. The sludge granulation process started after 120 days from the start-up period. Sludge granules size was found to be 0 8 mm at OLR of 1 72 kgCOD/(m 3·d), which reached maximum size of about 1 0 to 1 2 mm at OLR of 2 1 kgCOD/(m 3·d). At the end of initial OLR of 1 0 kgCOD/(m 3·d) the VSS concentration was 12 86 gVSS/L, which got increased to 38 05 gVSS/L at the end of an OLR 2 1 kgCOD/(m 3·d). Most of the times VFA recorded were well within the limit of VFA reported in anaerobic fermentation process. Many times the pH observed was between 6 5 and 7 8, which is more favorable for any anaerobic process. It is also found that pH within the reactor increases along with the height of reactor. The total maximum biogas production was found to be 0 40 L/gCOD removals at OLR of 2 1 kgCOD/(m 3·d) and the maximum BOD removal at this stage was observed to be 90%.

Thermal Hydrolysis of Wastewater Sludge Followed by Fungal Fermentation for Organic Recovery and Hyphae Fiber Production

Wastewater sludge creates a difficult environmental problem for many large cities.This study developed a three-phase innovative strategy for sludge treatment and reduction,including thermal hydrolysis,fungal fermentation,and anaerobic digestion.Increasing the temperature during the treatment from 140 to 180℃ significantly improved the sludge reduction and organic release efficiencies(p<0.05,one-way analysis of variance(ANOVA)for the triplicate experiments at each temperature).After two cycles of thermal hydrolysis,the overall volatile solid reduction ratios of the sludge were 36.6%,47.7%,and 58.5%for treatment at 140,160,and 180℃,respectively,and the total organic carbon(TOC)conversion efficiency reached 28.0%,38.0%,and 45.1%,respectively.The highest concentrations of carbohydrates and proteins were obtained at 160℃ in sludge liquor,whereas the amount of humic substances significantly increased for the treatment at 180℃(p<0.05,one-way ANOVA for the triplicate experiments at each temperature)due to the Maillard reaction.Fungal fermentation of the hydrolyzed sludge liquor with Aspergillus niger converted the waste organics to valuable fiber materials.The biomass concentration of fungal hyphae reached 1.30 and 1.27 g·L^(-1) in the liquor of sludge treated at 140 and 160C,corresponding to organic conversion ratios of 24.6%and 24.0%,respectively.The fungal hyphae produced from the sludge liquor can be readily used for making papers or similar value-added fibrous products.The paper sheets made of hyphae fibers had a dense structure and strong strength with a tensile strength of 10.75 N·m·g^(-1).Combining fungal fermentation and anaerobic digestion,the overall organic utilization efficiency can exceed 75%for the liquor of sludge treated at 160℃.

Anionic polyacrylamide alleviates cadmium inhibition on anaerobic digestion of waste activated sludge

The uncontrolled discharge of industrial wastewater leads to a significant cadmium(Cd)accumulation in waste activated sludge(WAS),posing a serious threat to the steady operation of the anaerobic digestion(AD)system in wastewater treatment plants(WWTPs).Therefore,developing a viable approach to cope with the adverse effects of high-concentration Cd on the AD system is urgently required.This study aims to investigate the potential of using anionic polyacrylamide(APAM),a commonly used agent in WWTPs,to mitigate the adverse effects of Cd in a toxic amount(i.e.,5.0 mg per g total suspended solids(TSS))on AD of WAS.The results showed that the effectiveness of higher APAM on Cd toxicity alleviation was less than that of lower APAM at the studied level(i.e.,the effectiveness order was 1.5 mg APAM per g TSS>3.0 mg APAM per g TSS>6.0 mg APAM per g TSS).The moderate supplement of APAM(i.e.,1.5 mg per g TSS)recovered the accumulative methane yield from 190.5±3.6 to 228.9±4.1 mL per g volatile solids by promoting solubilization,hydrolysis,and acidification processes related to methane production.The application of APAM also increased the abundance of key microbes in the AD system,especially Methanolinea among methanogens and Caldilineaceae among hydrolyzers.Furthermore,APAM facilitated the key enzyme activities involved in AD processes and reduced reactive oxygen species(induced by Cd)production via adsorption/enmeshment of Cd by APAM.These findings demonstrate the feasibility of using moderate APAM to mitigate Cd toxicity during AD,providing a promising solution for controlling Cd or other heavy metal toxicity in WWTPs.

STUDY ON MAXIMUM SPECIFIC SLUDGE ACTIVITY OF DIFFERENT ANAEROBIC GRANULAR SLUDGE BY BATCH TESTS

The maximum specific sludge activity of granular sludge from large scale UASB, IC and Biobed anaerobic reactors were investigated by batch tests. The limitation factors related to maximum specific sludge activity (diffusion, substrate sort, substrate concentration and granular size) were studied. The general principle and procedure for the precise measurement of maximum specific sludge activity were suggested. The potential capacity of loading rate of the IC and Biobed anaerobic reactors were analyzed and compared by use of the batch tests results.

Studies on the effects of pretreatment on production hydrogen from municipal sludge anaerobic fermentation

Municipal sludge was rich in organic matter, period of natural degradation was long and low efficiency, leachate would pollute underground water. In this paper, a comparative study of the ways of pretreatment with acid alkali treatment, heat digestion and ultrasonic treatment were done. The results showed that The dehydro-genase activity were increased, the SCOD (soluable chemical oxygen demand, SCOD) in-creased more than 2.47~2.83, 1.70~1.76, 2.6~ 2.77 times respectively. The hydrogen yield in-creased more than 11.5~12.2, 24.1~24.7, 34.2~ 34.9 mL.g-1 (VS) respectively. The period of pro- hydrogen was shorten to 7.5, 8.0, 6.5 d respec-tively. The degradation rate was up to 72.04%, 81.4%, 80% respectively, the methane concen-tration in the gas was close to “zero” and ul-trasonic treatment was better than others. Gompertz model curve fitting on hydrogen production was carried out. All the values of correlation factor R2 were more than 0.97.

Pre-treatment to Enhance Biogas Yield from Pulp and Paper Mill Sludge

The purpose of this work was to study the potential to enhance biogas production from pulp and paper mill sludge by the use of thermal pre-treatment in combination with chemical pre-treatment. Biogas from waste is a renewable fuel with very low emissions during combustion. To further reduce the use of fossil fuels, more biogas substrates are necessary. Pulp and paper mill sludge is a large untapped reservoir of potential biogas. Pulp and paper mill sludge was collected from a mill that produces both pulp and paper and has a modified waste activated sludge system as part of its wastewater treatment. Pre-treatments were chosen heat （70 ~C or 140℃） combined with either acid （pH 2 or pH 4） or base （pH 9 or pH 11, obtained with Ca（OH）2 or NaOH）. Biogas potential was tested by anaerobic digestion batch assays under mesophilic conditions. All pre-treatments were tested in six replicates. Biogas volume was measured with a gas-tight syringe and methane concentration was measured with a gas chromatograph. The methane yield from sludge subjected to thermal pre-treatment at 70℃ did not differ from the untreated sludge, but thermal pre-treatment at 140℃ had a positive effect. Within the 70℃ thermal pre-treatment group, the pH 2 acid was the most successful chemical pre-treatment, and Ca（OH）2 pH 9 had the least effect with no measurable improvement in methane yield. For the 140 ℃ thermal pre-treatment group, acid and NaOH impacted methane production negatively, while the Ca（OH）2-treated sludge did not differ from sludge with no chemical pre-treatment. In conclusion, thermal pre-treatment at 70℃ showed no effect, whereas, pre-treatment at 140℃ improved methane yield with 170%, and for this sludge additional, chemical pre-treatments are unnecessary.

Effects of treatment time and temperature on the DC corona pretreatment performance of waste activated sludge

In order to improve the anaerobic digestion efficiency of waste activated sludge（WAS）,a pretreatment procedure should be carried out so as to disrupt the microbial cell structure,thus releasing intracellular organic matters.In this paper,a corona discharge triggered by a DC voltage was employed to pre-treat WAS for various time periods under different temperatures.The magnitude of the DC voltage was 4 k V at both negative and positive polarities.The changes in the soluble chemical oxygen demand,phosphorus and nitrogen content,and p H value within the WAS were utilized to estimate the pretreatment performance of the DC corona.It was found that with increasing treatment time,the pretreatment efficiency tends to be reduced.With increased temperature,the pretreatment efficiency appears to be better.It is suggested that the oxidative species and the active particles generated in the corona discharge play an important role in disrupting the microbial cell structure,which is dependent upon the treatment time and the temperature.

Optimization of Methane Production Based on Mixture Content of Sewage Sludge, Food Waste, and Glycerol

This paper presents bench scale experiments related to anaerobic co-digestion of aerobic sewage sludge from a pilot WWTP （waste water treatment plants）, raw glycerol from a biodiesel industry and food waste. Assays were conducted in 100 mL non-stirring penicillin vessels, at 30 ℃ and planned according to three optimization phases： （1） binary mixture of sewage sludge and FW （food waste）; （2） binary mixture of sewage sludge and glycerol; and （3） ternary mixture of sewage sludge, FW, and glycerol. In the first and second phases, the highest SMP （specific methane production） was achieved by 10% （v/v） FW and 0.5% （v/v） glycerol mixtures. The optimization of the ternary mixture during the third phase was reached by the combination of 10% （v/v） FW and 0.4% （v/v） glycerol. Despite the low SMP value, the addition of glycerol and FW contributed to doubling the SMP value of the sludge sample control.

Effect of nitrite on hydrolysis-acidification, biogas production and microbial community in semi-continuous two-phase anaerobic digestion of sewage sludge

Previous study found that the pre-treatment of sewage sludge with nitrite improves the biogas production during the mono/two-phase anaerobic digestion (AD) using batch biochemical methane potential tests.In this study,the effects of nitrite on hydrolysisacidification,biogas production,volatile solids destruction and microbial composition in semi-continuous two-phase AD of sewage sludge were investigated.The addition of nitrite promotes sludge organic matter solubilization (+484%) and VFAs production (+98.9%),and causes an increase in the VS degradation rate during the AD process (+8.7%).The comparison of biogas production from the acidogenic and methanogenic reactors with or without the addition of nitrite implies that the nitrite has no significant effect on the overall biogas production of two-phase sludge AD process.High-throughput sequencing analysis shows that the microbial communities of bacteria and archaea in two-phase AD reactors significantly changes after the addition of nitrite.Vulcanibacillus (bacteria) and Candidatus Methanofastidiosum (archaea) become the dominant genera in the acidogenic and methanogenic reactors with the nitrite respectively.These findings provide new insights about using nitrite to promote the organic matter degradation of sewage sludge in a semicontinuous two-phase AD system.

Characteristics of high-sulfate wastewater treatment by two-phase anaerobic digestion process with Jet-loop anaerobic fluidized bed

A new anaerobic reactor, Jet-loop anaerobic fluidized bed （JLAFB）, was designed for treating high-sulfate wastewater. The treatment characteristics, including the effect of influent COD/SO42 ratio and alkalinity and sulfide inhibition in reactors, were discussed for a JLAFB and a general anaerobic fiuidized bed （AFB） reactor used as sulfate-reducing phase and methane-producing phase, respectively, in two-phase anaerobic digestion process. The formation of granules in the two reactors was also examined. The results indicated that COD and sulfate removal had different demand of influent COD/SO4^2- ratios. When total COD removal was up to 85%, the ratio was only required up to 1.2, whereas, total sulfate removal up to 95% required it exceeding 3.0. The alkalinity in the two reactors increased linearly with the growth of influent alkalinity. Moreover, the change of influent alkalinity had no significant effect on pH and volatile fatty acids （VFA） in the two reactors. Influent alkalinity kept at 400-500 mg/L could meet the requirement of the treating process. The JLAFB reactor had great advantage in avoiding sulfide and free-H2S accumulation and toxicity inhibition on microorganisms. When sulfate loading rate was up to 8. 1 kg/（m^3.d）, the sulfide and free-H2S concentrations in JLAFB reactor were 58.6 and 49.7 mg/L, respectively. Furthermore, the granules, with offwhite color, ellipse shape and diameters of 1.0-3.0 mm, could be developed in JLAFB reactor. In granules, different groups of bacteria were distributed in different layers, and some inorganic metal compounds such as Fe, Ca, Mg etc. were found.

Startup and operation of anaerobic EGSB reactor treating palm oil mill effluent

A bench-scale expanded granular sludge bed （EGSB） reactor was applied to the treatment of palm oil mill effluent （POME）. The reactor had been operated continuously at 35℃ for 514 d, with organic loading rate （OLR） increased from 1.45 to 17.5 kg COD/（m^3·d）. The results showed that the EGSB reactor had good performance in terms of COD removal on the one hand, high COD removal of 91% was obtained at two days＇ of hydraulic retention time （HRT）, and the highest OLR of 17.5 kg COD/（m^3·d）. On the other hand, only 46% COD in raw POME was transformed into biogas in which the methane content was about 70% （V/V）. A 30-d intermittent experiment indicated that the maximum transformation potential of organic matter in raw POME into methane was 56%. Volatile fatty acid （VFA） accumulation was observed in the later operation stage, and this was settled by supplementing trace metal elements. On the whole, the system exhibited good stability in terms of acidity and alkalinity. Finally, the operational problems inherent in the laboratory scale experiment and the corresponding countermeasures were also discussed.