Effects of Biowaste-Derived Hydrochar on Anaerobic Digestion:Insights into Hydrochar Characteristics

Hydrochar prepared with four typical biowastes,pine wood,food waste,digested sewage sludge,and Chlorella were applied for the promotion of anaerobic digestion.The gas production and substrate composition were analyzed associated with the hydrochar characteristics.The results suggested that Chlorella hydrochar(C-C)showed the highest cumulative yield of methane(approximately 345 mL)with high total organic carbon(TOC)removal efficiency and low volatile fatty acids(VAFs)concentration.Especially,food waste hydrochar(F-C)showed a poor effect on anaerobic digestion and aroused 1.4–1.6 g/L accumulation of VAFs,in which the toxic components may account for the low efficiency.The C-C and sludge hydrochar(S-C)may develop direct interspecific electron transport(DIET)to facilitate the generation of methane by both surface groups and conductivity of the body structure,unlike pinewood hydrochar(P-C),which mainly depended on the aromatic matrix structure of hydrochar body.This work suggested that C-C can be the best candidate for the facilitation of anaerobic digestion,and N-containing biowaste like algae and lignocellulose like pine wood may establish different DIET pathways based on the physicochemical characteristics of hydrochar.

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.

High-solid Anaerobic Co-digestion of Food Waste and Rice Straw for Biogas Production

Anaerobic co-digestion of food waste（FW） and rice straw（RS） in continuously stirred tank reactor（CSTR） at high organic loading rate（OLR） was investigated. Co-digestion studies of FW and RS with six different mixing ratios were conducted at an initial volatile solid（VS） concentration of more than 3 g VS · L-1. The biogas production, methane contents, degradation efficiency of VS, chemical oxygen demand（COD） and volatile fatty acids（VFAs） were determined to evaluate the stability and performance of the system. The results showed that the co-digestion process had higher system stability and higher volumetric biogas production than mono-digestions. Increase in FW content in the feedstock could increase the methane yield and shorten retention time. The efficiency of co-digestion systems mainly relied on the mixing ratios of FW and RS to some extent. The highest methane yield was 60.55 m L· g V· S-1 · d-1 at a mass ratio（FW/RS） of 3 ： 1, which was 178% and 70% higher than that of mono-digestions of FW and RS, respectively. Consequently, the anaerobic co-digestion of FW and RS could have superior stability and better performance than monodigestions in higher organic loading system.

High-solid anaerobic digestion of sewage sludge:achievements and perspectives

High-solid anaerobic digestion(HS-AD)has been applied extensively during the last few decades for treating various organic wastes,such as agricultural wastes,organic fractions of municipal solid wastes,and kitchen wastes.However,the application of HS-AD to the processing of sewage sludge(SS)remains limited,which is largely attributable to its poor process stability and performance.Extensive research has been conducted to attempt to surmount these limitations.In this review,the main factors affecting process stability and performance in the HS-AD of SS are comprehensively reviewed,and the improved methods in current use,such as HS sludge pre-treatment and anaerobic co-digestion with other organic wastes,are summarised.Besides,this paper also discusses the characteristics of substance transformation in the HS-AD of SS with and without thermal pre-treatment.Research has shown that the HS effect is due to the presence of high concentrations of substances that may inhibit the function of anaerobic microorganisms,and that it also results in poor mass transfer,a low diffusion coefficient,and high viscosity.Finally,knowledge gaps in the current research on HS-AD of SS are identified.Based on these,it proposes that future efforts should be devoted to standardising the definition of HS sludge,revealing the law of migration and transformation of pollutants,describing the metabolic pathways by which specific substances are degraded,and establishing accurate mathematical models.Moreover,developing green sludge dewatering agents,obtaining high value-added products,and revealing effects of the above two on HS-AD of SS can also be considered in future.

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.

Stable Control of Influence Factor during Two-phase Anaerobic Digestion for Agricultural Organic Waste

Two-phase anaerobic digestion process is influenced by acid control for hydrogen production, reaction temperature, substrate detention time, sludge activity, and granular formation. Al of these technological parameters are directly related to success or failure of the system operation and treatment effect.

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.

Start-up performances of dry anaerobic mesophilic and thermophilic digestions of organic solid wastes

Two dry anaerobic digestions of organic solid wastes were conducted for 6 weeks in a lab-scale batch experiment for investigating the start-up performances under mesophilic and thermophilic conditions. The enzymatic activities, i.e., β-glucosidase, N-α-benzoyl-Largininamide （BAA）-hydrolysing protease, urease and phosphatase activities were analysed. The BAA-hydrolysing protease activity during the first 2-3 weeks was low with low pH, but was enhanced later with the pH increase. β-Glucosidase activity showed the lowest values in weeks 1-2, and recovered with the increase of BAA-hydrolysing protease activity. Acetic acid dominated most of the total VFAs in thermophilic digestion, while propionate and butyrate dominated in mesophilic digestion. Thermophilic digestion was confirmed more feasible for achieving better performance against misbalance, especially during the start-up period in a dry anaerobic digestion process.

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.

Influence of lactic acid on the two-phase anaerobic digestion of kitchen wastes

To evaluate the influence of lactic acid on the methanogenesis, anaerobic digestion of kitchen wastes was firstly conducted in a two-phase anaerobic digestion process, and performance of two digesters fed with lactic acid and glucose was subsequently compared. The results showed that the lactic acid was the main fermentation products of hydrolysis-acidification stage in the two-phase anaerobic digestion process for kitchen wastes. The lactic acid concentration constituted approximately 50% of the chemical oxygen demand （COD） concentration in the hydrolysis-acidification liquid. The maximum organic loading rate was lower in the digester fed with lactic acid than that fed with glucose. Volatile fatty acids （VFAs） and COD removal were deteriorated in the methanogenic reactor fed with lactic acid compared to that fed with glucose. The specific methanogenic activity （SMA） declined to 0.343 g COD/（gVSS-d） when the COD loading were designated as 18.8 g/（L-d） in the digester fed with lactic acid. The propionic acid accumulation occurred due to the high concentration of lactic acid fed. It could be concluded that avoiding the presence of the lactic acid is necessary in the hydrolysis-acidification process for the improvement of the two-phase anaerobic digestion process of kitchen wastes.

Influence of temperature on performance of anaerobic digestion of municipal solid waste

The influence of temperature on the performance of anaerobic reactors for treating the organic fraction of municipal sohd waste （OFMSW） was studied. Batch digestion of OFMSW was carded out for 32 d at different temperature （25℃, 35℃, 45℃ and 55℃） conditions for total solid concentrations （TS） 17% with the ratio of total organic carbon to nitrogen （C/N） being, 25：1 respectively, while keeping other parameters constant such as inoculum, start-up pH, reactor volume （2 L） and so on. Temperature can influence the methanogenic bacteria activity, accordingly inhibiting the OFMSW biodegradation and stabilization efficiency. Anaerobic reactors excelled at TS reduction, total volatile solid reduction, chemical oxygen demand reduction, increasing cumulative biogas production, whose rate was at temperature （35℃ and 55℃） conditions. Methane concentration in the biogas was above 65% in four reactors. In addition, the fluctuation of temperatures resulted in the biogas production variation. The data obtained indicated that temperature had a significant influence on anaerobic process.

Wheat straw pretreatment with KOH for enhancing biomethane production and fertilizer value in anaerobic digestion

Wheat straw biodegradability during anaerobic digestion was improved by treatment with potassium hydroxide （KOH） to decrease digestion time and enhance biomethane production and fertility value. KOH concentrations of 1% （KI）, 3% （[（2）, 6% （K3） and 9% （l（4） were tested for wheat straw pretreatment at ambient temperature with a C：N ratio of 25：1.86% of total solids （TS）, 89% of volatile solids （VS） and 22% of lignocellulose, cellulose and hemi- cellulose （LCH） （22%） were decomposed effectively with the wheat straw pretreated by 6% KOH. Enhanced bio- gas production and cumulative biomethane yield of 258 ml. （g VS）-1 were obtained increased by 45% and 41% respectively, compared with untreated wheat straw. Pretreated wheat straw digestion also yielded a digestate with higher fertilizer values potassium （l 38%）, calcium （22%） and magnesium （16%）. These results show that TS, VS and LCH can be effectively removed from wheat straw pretreated with KOH, improving biodegradability biomethane production and fertilizer value.

Effects of Oxytetracycline on Methane Production and the Microbial Communities During Anaerobic Digestion of Cow Manure

The effects of different concentrations of oxytetracycline （OTC） on the dynamics of bacterial and archaeal communities during the mesophilic anaerobic digestion （37＆#176;C） of cow manure were investigated. Before anaerobic digestion, OTC was added to digesters at concentrations of 20, 50, and 80 mg L-1, respectively. Compared with no-antibiotic control, all methane productions underwent different levels of inhibition at different concentrations of OTC. Changes in the bacterial and archaeal communities were discussed by using PCR-denaturing gradient gel electrophoresis （DGGE）. Results showed that OTC affected the richness and diversity of bacterial and archaeal communities. The bacterial genus Flavobacterium and an uncultured bacterium （JN256083.1） were detected throughout the entire process of anaerobic digestion and seemed to be the functional bacteria. Methanobrevibacter boviskoreani and an uncultured archaeon （FJ230982.1） dominated the archaeal communities during anaerobic digestion. These microorganisms may have high resistance to OTC and may play vital roles in methane production.

Effect on anaerobic digestion performance of corn stover by freezing–thawing with ammonia pretreatment

In order to enhance the biomethane production from corn stover, choosing effective pretreatment is one of the necessary steps before starting anaerobic digestion(AD).This study was aimed to analyze the effectiveness of freezing–thawing with ammonia pretreatment on substance degradation and AD performance of corn stover.Three ammonia concentrations(2%, 4%, and 6%) with two different moisture contents(50% and 70%) were used to pretreat the corn stover at two temperatures(-20 ℃ and 20 ℃).The result showed that an optimum pretreatment condition for corn stover was at the temperature of -20 ℃, moisture content of 70% and ammonia concentration of 2%.Under the optimum pretreatment condition, the maximum biomethane yield reached 261 ml·(g VS)^(-1), which was 41.08% higher than that of the untreated.Under different pretreatment conditions,the highest loss of lignin at -20 ℃ with 2% ammonia concentration was 63.36% compared with the untreated.The buffer capacity of AD system was also improved after the freezing–thawing with ammonia pretreatment.Therefore, the freezing–thawing with ammonia pretreatment can be used to improve AD performance for corn stover.This study provides further insight for exploring an efficient freezing–thawing with ammonia pretreatment strategy to enhance AD performance for the practical application.

The relationships among sCOD, VFAs, microbial community, and biogas production during anaerobic digestion of rice straw pretreated with ammonia

This study investigated the effects of soluble chemical oxygen demand(s COD),volatile fatty acids(VFAs),and microbial community on biogas production in the process of rice straw(RS)anaerobic digestion(AD).The results showed that the s COD concentrations and VFA production appeared the same trend,which was inversely related with that of daily biogas production.The cumulative methane yield of RS was 194.9 ml·(g VS)^-1·^-1.The modified Gompertz model is the best fit for measured methane yields of RS in the three kinetic models of first-order kinetic,Cone and modified Gompertz.Firmicutes,Bacteroidetes,and Euryarchaeota were the dominant microbial phyla throughout AD process.At the genus level,the microorganisms mainly composed of Clostridium,Vadin,Terrisporobacter,Methanosaeta,Methanobacterium,and Methanosarcina.Proteiniphilum showed strong relationship with s COD and VFA production.Clostridium and Terrisporobacter displayed relationship with biogas production.Therefore,in order to improve the stability of the AD system,the parameter changes of VFAs,s COD,and biogas yield were monitored in the RS AD process.The study can provide theoretical basis for improving the efficiency of RS AD.

Effects of Different States of Fe on Anaerobic Digestion:A Review

Anaerobic digestion is widely used in the treatment of industrial wastewater,excess activated sludge,municipal waste,crop straw and livestock manure,with the functions of environmental protection and energy recovery. This review summarizes and evaluates the present knowledge of effects of different states of Fe( ZVI,Fe( II),Fe( III)) on hydrogen and methane production in anaerobic digestion process. The potential promotion effects of iron oxides nanoparticles( IONPs),especially magnetite nanoparticles on anaerobic digestion are also mentioned. Fe plays important role in transporting electron,stimulating bacterial growth and increasing hydrogen and methane production rate by promoting enzyme activity. Adding Fe with different morphologies and valence states in anaerobic digestion to increase biogas( hydrogen and methane) production and enhance organic matter degradation simultaneously,which has attracted many scientists' attention in recent years. Rapid progress in this area has been made over the last few years,since Fe is essential to the fermentative hydrogen and methane production,while few is known about how Fe affects the fermentative biogas production. This review is significant to maintain the stable operation of the biogas project.

Improving physicochemical characteristics and anaerobic digestion performance of rice straw via ammonia pretreatment at varying concentrations and moisture levels

Rice straw physicochemical characteristics and anaerobic digestion(AD)performance via ammonia pretreatment at varying ammonia concentrations(2%,4%,and 6%)and moisture contents(30%,50%,70%,and 90%)under a mild condition were investigated.The results showed that the ammonia pretreatment effectively damaged the rice straw structure,increased the soluble organic concentration,and improved rice straw hydrolysis and AD performance.After pretreatment,the ester bond and ether bond were ruptured in lignocellulose and the volatile fatty acids(VFAs)were within the range of 1457.81–1823.67 mg·L-1.In addition,ammonia pretreatment had high selectivity on lignin removal,resulting in a maximum lignin removal rate of 50.80%.The highest methane yield of rice straw was 250.34 ml·(g VS)-1 at a 4%ammonia concentration coupled with a 70%moisture content,which was 28.55%higher than that of the control.The result showed that ammonia pretreatment of rice straw is technically suitable to enhance AD performance for further application.

Combined pretreatment using CaO and liquid fraction of digestate of rice straw: Anaerobic digestion performance and electron transfer

To improve anaerobic digestion(AD)efficiency of rice straw,solid alkaline CaO and the liquid fraction of digestate(LFD)were used as pretreatment agents of rice straw.The results showed that AD performance of rice straw with CaOLFD pretreatment was optimal in different pretreatment methods of the CaO+LFD,CaOLFD,LFD+CaO,CaO,and LFD.The maximum methane yield(314 ml(g VS)^(-1))and the highest VFAs concentration(14851 mg·L^(-1) on day 3)of the CaOLFD pretreatment group were 81%and 118%higher than that of the control group,respectively.Under the action of solid alkaline CaO,the bacteria of Clostridium,Atopostipes,Sphaerochaeta,Tissierella,Thiopseudomonas,Rikenellaceae,and Sedimentibacter could build up co-cultures with the archaeal of Methanosaeta,Methanobacterium,and Methanosarcina performing direct interspecies electron transfer(DIET)and improving AD performance of rice straw.Therefore,the combined pretreatment using CaO and LFD could not only pretreat rice straw but also stimulate co-cultures of microorganism to establish DIET enhancing AD efficiency.

Biogas Production from Anaerobic Digestion of High Oil Waste

The possibility of anaerobic digestion of high oil waste at high temperatures was explored,and the effects of fat concentration on biogas production via anaerobic digestion were analyzed by batch and continuous experiments successively. Besides,the response and recovery of the digestion system to the shock of high concentrations of oil were studied. The results showed that the anaerobic digestion of high oil waste could be carried out,and fat concentration had a significant effect on the anaerobic digestion. In the batch experiments,the process of anaerobic digestion could carry out only when fat concentration was 0-1. 68%,and the average methane content was 46. 42%; with the increase of fat concentration,both methane content and production rate decreased significantly,and the digestion period was extended obviously. When fat concentration exceeded 2. 52%,the anaerobic digestion failed to start,and methane could not be detected in the produced biogas. In the continuous experiments,the system could withstand a certain concentration of fat( 6 g/L),and anaerobic digestion process would be inhibited when it experienced the impact of a high oil load( 26. 7 g/L). Nevertheless,this process could recover quickly after the removal of the impact,and the system could withstand a higher fat concentration( 13 g/L) than before. Furthermore,the volume production rate of biogas was approximately 1 L/( L·d),and methane content was about 55%.

The Role of Biochar to Enhance Anaerobic Digestion: A Review

Biochar,one of the products of thermochemical conversion of biomass,possesses specific physiochemical properties such as conductivity,pore adsorption,surface functional groups,and cation exchange capacity.Anaerobic digestion(AD)as a classical bio-wastes conversion technology,suffers from inhibitions,process instability,and methanogenic inefficiency which limit its efficiency.With the advantages of pH buffering,functional microbes enrichment,inhibitors alleviating,and direct interspecies electron transfer(DIET)accelerating,biochar suggests a promising application as additives for AD.Herein,this paper reviewed the noting physicochemical properties of biochar,and discussed its roles and related mechanisms in AD.Further,this paper highlighted the advantages and drawbacks,and pointed out the corresponding challenges and prospects for future research and application of biochar amending AD.