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.

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℃.

Sludge composition and characteristics shaped microbial community and further determined process performance: A study on full-scale thermal hydrolysis-anaerobic digestion processes

Anaerobic digestion (AD) with thermal hydrolysis (TH) pretreatment is a promising process for excess sludge treatment,while there lacks of the knowledge from full-scale process about the impact of sludge composition and characteristics on microbial community and performance.The sludge physiochemical indices,microbial community and performance data of four full-scale TH-AD plants were characterized,and their relationships was elucidated.The four plants were operated under almost similar total organic loading rate (OLR)but their methanogenesis performance differentiate into two groups,namely superior group(SupG) and the inferior group (Inf G).In both groups,TH effectively solubilized particulate organic compounds,meanwhile raised the ammonia nitrogen (NH_(4)^(+)-N) and volatile fatty acid (VFA) concentration.Compared with the Sup G,thermal hydrolyzed sludge of Inf G had higher level of VFAs,NH_(4)^(+)-N and total chemical oxygen demand (t COD),which showed higher inhibition effect on microbes,leading to a community with lower diversity,lower abundance of carbohydrate degrading functional guild,higher protein degrading one,and methanogens that adapted to limited substrates,and further declined the methane production rate.Thus,it was recommended that OLR alone was not sufficient for controlling the system in design and operation,the concentration of VFAs,NH_(4)^(+)-N and t COD should be equally considered.Their higher concentration,together with the higher abundance of Defluviitoga and Proteiniphilum were recommended as indicators for inferior running condition.Our results proposed that microbial communities played a role of bridge between environmental factors and performance,provided implications for engineering ecology and operational regulation for full-scale sludge TH-AD process.

Comparison of mesophilic and thermophilic anaerobic digestions of thermal hydrolysis pretreated swine manure: Process performance,microbial communities and energy balance

Anaerobic digestion (AD) of swine manure (SM) commonly shows low biogas output and unsatisfactory economic performance. In this study, thermophilic AD (TAD, 50±1℃) was combined with thermal hydrolysis pretreatment (THP, 170℃/10 bar), to investigate its potential for maximizing biogas yield, securing successful digestion and microbial diversity, as well as improving energy balance. Four lab-scale continuously stirred tank reactors were operated for 300 days and compared with each other, i.e., reactor 1 (raw SM fed in mesophilic AD:RSM-MAD), reactor 2 (THP-treated SM fed in MAD:TSM-MAD), reactor 3 (RSM-TAD),and reactor 4 (TSM-TAD). The results showed that THP was efficient to increase methane production of SM, TSM-TAD mode led to the highest methane yield (129.8±40.5 mL-CH_(4)/gVS/day) among the tests (p <0.05). Although TAD was more likely to induce free ammonia (> 700 mg/L) or volatile fatty acids (> 6000 mg/L) accumulation compared with MAD in start-up phase, TSM-TAD treatment mode behaved a sustainable digestion process in a long-term operation. For TSM-TAD scenario, higher Shannon–Weaver (3.873) and lower Simpson index (0.061) indicated this mode ensured and enlarged the diversity of bacteria communities. Phylum Bathyarchaeota was dominant (59.3%-90.0%) in archaea community,followed by Euryarchaeota in the four reactors. RSM-MAD treatment mode achieved the highest energy output (4.65 GJ/day), TSM-TAD was less effective (-17.38 GJ/day) due to increased energy demands. Thus improving the energetic efficiency of THP units is recommended for the development of TSM-TAD treatment mode.

Preliminary Study on the Treatment Efficiency of Pasteurized Lime Thermal Alkaline Hydrolysis for Excess Activated Sludge and Reduction of Tetracycline Resistance Genes

Thermal alkaline hydrolysis is a common pretreatment method for the utilization of excess activated sludge(EAS).Owing to strict environment laws and need for better energy utilization,new methods were developed in this study to improve the efficiency of pretreatment method.Direct thermal hydrolysis(TH),pasteurized thermal hydrolysis(PTH),and alkaline pasteurized thermal hydrolysis(PTH+CaO and PTH+NaOH)methods were used to treat EAS.Each method was compared and analyzed in terms of dissolution in ammonium nitrogen(NH_(4)^(+)-N)and soluble COD(SCOD)in EAS.Furthermore,the removal of tetracycline resistance genes(TRGs)and class 1 transposon gene intI1 from EAS was investigated.The NH_(4)^(+)-N and SCOD concentrations in EAS treated by PTH were 1.24 and 2.58 times higher than those of TH.However,the removal efficiency of total TRGs and intI1 between the groups was comparable.The SCOD concentration of the PTH+NaOH group was 4.37 times higher than that of the PTH group,and the removal efficiency of total TRGs was increased by 9.52%compared with that by PTH.The NH_(4)^(+)-N and SCOD concentrations of the PTH+CaO group could reach 85.04%and 92.14%of the PTH+NaOH group,but the removal efficiency of total TRGs by PTH+CaO was 19.78%lower than that by PTH+NaOH.Thus,to reduce the financial cost in actual operation,lime(CaO)can be used instead of a strong alkali(NaOH),and pasteurized steam at 70℃ instead of conventional high-temperature heating to treat EAS.This study provides a reference for the development of alkaline hydrolysis under moderate temperatures along with the removal of TRGs in EAS.

Increasing the performance of anaerobic digestion:Pilot scale experimental study for thermal hydrolysis of mixed sludge

The performance of a pilot plant operation combining thermal hydrolysis(170℃,30 min)and anaerobic digestion(AD)was studied,determining the main properties for samples of fresh mixed sludge,hydrolyzed sludge,and digested sludge,in order to quantify the thermal pretreatment performance(disintegration,solubilisation,and dewaterability)and its impact on the anaerobic digestion performance(biodegradability,volatile solids reduction,and digester rheology)and end product characteristics(dewaterability,sanitation,organic and nitrogen content).The disintegration achieved during the thermal treatment enhances the sludge centrifugation,allowing a 70%higher total solids concentration in the feed to anaerobic digestion.The digestion of this sludge generates 40%more biogas in half the time,due to the higher solids removal compared to a conventional digester.The waste generated can be dewatered by centrifugation to 7%dry solids without polymer addition,and is pathogen free.

Characterization of value-added chemicals derived from the thermal hydrolysis and wet oxidation of sewage sludge

We evaluated the effect of hydrothermal pretreatments,i.e.,thermal hydrolysis(TH)and wet oxidation(WO)on sewage sludge to promote resource recovery.The hydrothermal processes were performed under mild temperature conditions(140°C–180°C)in a high pressure reactor.The reaction in acidic environment(pH=3.3)suppressed the formation of the color imparting undesirable Maillard’s compounds.The oxidative conditions resulted in higher volatile suspended solids(VSS)reduction(~90%)and chemical oxygen demand(COD)removal(~55%)whereas TH caused VSS and COD removals of~65%and~27%,respectively at a temperature of 180°C.During TH,the concentrations of carbohydrates and proteins in treated sludge were 400–1000 mg/L and 1500–2500 mg/L,respectively.Whereas,WO resulted in solids solubilization followed by oxidative degradation of organics into smaller molecular weight carboxylic acids such as acetic acid(~400–500 mg/L).Based on sludge transformation products generated during the hydrothermal pretreatments,simplified reaction pathways are predicted.Finally,the application of macromolecules(such as proteins),VFAs and nutrients present in the treated sludge are also discussed.The future study should focus on the development of economic recovery methods for various value-added compounds.

Occurrence and migration of microplastics and plasticizers in different wastewater and sludge treatment units in municipal wastewater treatment plant

Microplastics(MPs)and plasticizers,such as phthalate esters(PAEs),were frequently detected in municipal wastewater treatment plants(MWTP).Previous research mainly studied the removal of MPs and PAEs in wastewater.However,the occurrence of MPs and PAEs in the sludge was generally ignored.To comprehensively investigate the occurrence and the migration behaviors of MPs and PAEs in MWTP,a series of representative parameters including the number,size,color,shape of MPs,and the concentrations of PAEs in wastewater and sludge were systematically investigated.In this study,the concentrations of MPs in the influent and effluent were 15.46±0.37 and 0.30±0.14 particles/L.The MP removal efficiency of 98.1%was achieved and about 73.8%of MPs were accumulated in the sludge in the MWTP.The numbers of MPs in the sludge before and after digestion were 4.40±0.14 and 0.31±0.01 particles/g(dry sludge),respectively.Fourier Transform Infrared Spectroscopy(ATR FT-IR)analysis showed that the main types of MPs were polyethylene terephthalate(PET),polypropylene(PP),polyethylene(PE),and polystyrene(PS).Six PAEs,including phthalate(DMP),diethyl phthalate(DEP),diisobutyl phthalate(DIBP),ortho dibutyl phthalate(DBP),butyl benzyl phthalate(BBP),and bis(2-ethyl)hexyl phthalate(DEHP),were detected in the MWTP.The concentrations of total PAEs(ΣPAEs)in the influent and effluent were 76.66 and 6.28μg/L,respectively.The concentrations ofΣPAEs in the sludge before and after digestion were 152.64 and 31.70μg/g,respectively.In the process of thermal hydrolysis,the number and size of MPs decreased accompanied by the increase of the plasticizer concentration.