Enhancement of thermophilic anaerobic digestion of thickened waste activated sludge by combined microwave and alkaline pretreatment

Pretreatment of thickened waste activated sludge （TWAS） by combined microwave and alkaline pretreatment （MAP） was studied to improve thermophilic anaerobic digestion efficiency. Uniform design was applied to determine the combination of target temperature （110-210°C）, microwave holding time （1-51 min）, and NaOH dose （0-2.5 g NaOH/g suspended solids （SS）） in terms of their effect on volatile suspended solids （VSS） solubilization. Maximum solubilization ratio （85.1%） of VSS was observed at 210°C with 0.2 g-NaOH/g-SS and 35 min holding time. The effects of 12 different pretreatment methods were investigated in 28 thermophilic batch reactors by monitoring cumulative methane production （CMP）. Improvements in methane production in the TWAS were directly related to the microwave and alkaline pretreatment of the sludge. The highest CMP was a 27% improvement over the control. In spite of the increase in soluble chemical oxygen demand concentration and the decrease in dewaterability of digested sludge, a semi-continuous thermophilic reactor fed with pretreated TWAS without neutralization （at 170~C with 1 min holding time and 0.05 g NaOH/g SS） was stable and functioned well, with volatile solid （VS） and total chemical oxygen demand （TCOD） reductions of 28% and 18%, respectively, which were higher than those of the control system. Additionally, methane yields （L@STP/g-CODaded, at standard temperature and pressure （STP） conditions of 0°C and 101.325 kPa） and （L@STP/g VSadad） increased by 17% and 13%, respectively, comoared to the control reactor.

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.

Effect of ultrasonic pretreatment on anaerobic digestion and its sludge dewaterability

To investigate the effect of ultrasonic pretreatment on anaerobic digestion and sludge dewaterability and further to probe into the influencing factors on sludge dewaterability,sludge flocs were stratified into four fractions： （1） slime;（2） loosely bound extracellular polymeric substances （LB-EPS）;（3） tightly bound EPS （TB-EPS）;and （4） EPS-free pellets.The results showed that ultrasonic pretreatment increased the anaerobic digestion efficiency by 7%–8%.Anaerobic digestion without ultrasonic pretreatment deteriorated the sludge dewaterability,with the capillary suction time （CST） increased from 1.42 to 47.3 （sec·L）/g-TSS.The application of ultrasonic pretreatment firstly deteriorated the sludge dewaterability （normalized CST increased to 44.4 （sec·L）/g-TSS）,while subsequent anaerobic digestion offset this effect and ultimately decreased the normalized CST to 23.2 （sec·L）/g-TSS.The dewaterability of unsonicated sludge correlated with protein （p = 0.003） and polysaccharide （p = 0.004） concentrations in the slime fraction,while that of sonicated sludge correlated with protein concentrations in the slime and LB-EPS fractions （p 0.05）.Fluorescent excitationemission matrix analysis showed that the fluorescence matters in the LB-EPS fraction significantly correlated with sludge dewaterability during anarobic digestion.

Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline, thermal hydrolysis and ultrasonic pretreatments

Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%-75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.

Enhanced nitrogen removal upon the addition of volatile fatty acids from activated sludge by combining calcium peroxide and low-thermal pretreatments

This study investigated a combined low-thermal and CaO_(2)pretreatment to enhance the volatile fatty acid(VFA)production from waste activated sludge(WAS).The fermentative product was added to a sequencing batch reactor(SBR)as an external carbon source to enhance nitrogen removal.The results showed that the combined pretreatment improved WAS solubilization,releasing more biodegradable substrates,such as proteins and polysaccharides,from TB-EPS to LB-EPS and S-EPS.The maximum VFA production of 3529±188 mg COD/L was obtained in the combined pretreatment(0.2 g CaO_(2)/g VS+70℃for 60 min),which was 2.1 and 1.4-fold of that obtained from the sole low-thermal pretreatment and the control test,respectively.Consequently,when the fermentative liquid was added as an external denitrification carbon source,the effluent total nitrogen decreased to Class A of the discharge standard for pollutants in rural wastewater treatment plants in most areas of China.

Waste sludge disintegration, methanogenesis and final disposal via various pretreatments: Comparison of performance and effectiveness

This study compared the three wastewater pretreatments of ozonation,Fe2þ-S2O82and freeze-thawing(F/T)in the disintegration,anaerobic digestion(AD)and final disposal of the sludge.The F/T pretreatment increased the dewaterability and settleability of the sludge by 7.8%and 47.1%,respectively.The ozonation pretreatment formed more volatile fatty acids(VFAs),with a peak value of 320.82 mg SCOD/L and controlled the release of sulfides.The Fe2þ-S2O82pretreatment removed heavy metals through the absorption and flocculation of ferric particles formed in-situ.During the anaerobic digestion of the sludge,the ozonation pretreatment accelerated the hydrolysis rate(k)rather than the biochemical methane potential(B0)of the sludge due to the high VFA content in the supernatant.Comparatively,the F/T pretreatment facilitated the B0 with great economic efficiency by enhancing the solubilisation of the sludge.Although Fe2þ-S2O82pretreatment decreased the methane production,the ferric particle was a unique advantage in the disintegration and harmless disposal of the sludge.The digested sludge had more VFAs after ozonation pretreatment,which contributed to the recycling of carbon.In addition,the lower sludge volume could save the expense of transportation and disposal by ozonation pretreatment.Different pretreatments had different characteristics.The comparative study provided information allowing the selection of the type of pretreatment to achieve different objectives of the treatment and disposal of sludge.

Overview of key operation factors and strategies for improving fermentative volatile fatty acid production and product regulation from sewage sludge

In recent years,volatile fatty acid(VFA)production through anaerobic fermentation of sewage sludge,instead of methane production,has been regarded as a high-value and promising roadmap for sludge stabilization and resource recovery.This review first presents the effects of some essential factors that influence VFA production and composition.In the second part,we present an extensive analysis of conventional pretreatment and co-fermentation strategies ultimately addressed to improving VFA production and composition.Also,the effectiveness of these approaches is summarized in terms of sludge degradation,hydrolysis rate,and VFA production and composition.According to published studies,it is concluded that some pretreatments such as alkaline and thermal pretreatment are the most effective ways to enhance VFA production from sewage sludge.The possible reasons for the improvement of VFA production by different methods are also discussed.Finally,this review also highlights several current technical challenges and opportunities in VFA production with spectrum control,and further related research is proposed.

基于文献计量学分析的剩余污泥厌氧消化预处理研究进展

污水处理过程中会产生大量剩余污泥,对剩余污泥进行厌氧消化处理既能减少环境污染,又能回收能源。本文基于文献计量学方法和可视化工具,对中国知网(CNKI)数据库和Web of Science核心数据库2003—2023年间收录的相关文章进行梳理,对当前剩余污泥厌氧消化处理的研究热点领域进行比较分析,并对剩余污泥成分、理化特性和厌氧消化预处理方法进行文献综述。研究表明,剩余污泥厌氧消化产生甲烷是该处理技术的重要目的,预处理技术与剩余污泥处理存在重要关联性;物理、化学和生物酶等不同预处理技术对产沼气量有较大影响,针对污泥本身的理化性质而采用更加合适的预处理技术,能够在节约成本的同时进一步提高剩余污泥资源化利用程度。

超声波-游离亚硝酸联合预处理污泥强化厌氧消化的机制解析

本研究对超声波(US)预处理、游离亚硝酸(FNA)预处理及超声波-游离亚硝酸(USFNA)联合预处理对于污泥有机质溶出、絮体分散、细胞内容物释放及产甲烷性能的作用进行评估。结果表明,US预处理的主要作用是使絮体分散与胞外聚合物溶出,FNA预处理则是使细胞内容物释放。US-FNA联合预处理后,污泥甲烷产率较未预处理增加了37.1%,分别达到US预处理的1.07倍和FNA预处理的1.08倍,但US与FNA在联合预处理中所发挥作用各自独立,并未发现明显的协同增效作用。引入FNA会降低污泥厌氧消化初期产气速率,未对累积产气量造成显著影响。根据发酵后污泥微生物菌群的解析,发现FNA是影响污泥微生物多样性的主导因素。

污泥碱解和超声破解预处理的效果研究

为提高污水厂污泥的厌氧消化速率,采用多频率多功率槽式超声发生器,研究了超声波、碱解、以及两者的组合作用对污泥破解预处理效果的影响.结果表明,碱和超声波的组合预处理方式,对污泥溶解性COD的释放效果和VSS减少效果明显优于单独的超声波和单独的碱处理.单独超声预处理,污泥VSS的最大减少率为15.98%;单独碱解(NaOH/TS=0.04)时为22.12%;先碱解(NaOH/TS=0.04,24 h),再超声(60 min)以及碱(NaOH/TS=0.04)和超声(60 min)同时作用的预处理方式,可将污泥VSS减少率分别提高到51.45%和54.45%.破解作用引起污泥的水解分为快速水解和缓慢水解2个阶段,对快速水解阶段进行动力学分析可知,同时采用碱和超声的预处理方式不但可以获得最高的水解速率,而且降低了碱的投加量,缩短了超声破解的时间.

污泥厌氧消化预处理方法研究进展

介绍了高压水流喷射法、碱溶法、超声波法、臭氧氧化法、γ-辐照法以及高能电子束辐照等污泥预处理方法的基本原理、特点及应用前景。

不同预处理方式对污泥厌氧发酵的影响

污水生物处理的应用产生了大量污泥,污泥的处理与处置已成为污水处理厂面临的一个重大挑战。填埋、焚烧等传统污泥处理方法,不仅污染环境而且消耗大量能源,而厌氧发酵处理作为一种可持续的污泥处理方法具有保护环境、节约能源等优点。传统的污泥厌氧发酵处理存在反应效率低、污泥降解性差、停留时间长等不足,污泥预处理在改善其厌氧发酵性能方面越来越受到关注。根据污泥的理化特性、厌氧发酵特点,论述了各类预处理方式的不同作用机制,分类比较了不同类型预处理的处理效果及其对污泥厌氧发酵特性的影响,深入分析了影响不同预处理强化污泥厌氧发酵的主要因素。同时,对其强化污泥厌氧发酵存在的不足及其今后的发展方向作了简要的分析和展望。

微波预处理剩余污泥的研究进展

介绍了微波预处理污泥的作用机理及作用过程,包括污泥絮体破解、污泥细胞破碎及有机物的释放、有机物水解、美拉德反应等,总结了微波预处理污泥的作用效果(物理特性、化学特性、生物特性)、影响微波预处理效果的因素(污泥特性、处理条件)和微波预处理污泥对其后续厌氧消化的影响。指出了目前研究中存在的主要问题是试验规模偏小,预处理方式为间歇处理,在对污泥中有毒有害有机物和病原微生物的去除研究方面还需加强。提出今后应重点开展微波组合工艺对污泥中有毒有害有机物和病原微生物去除的基础研究,同时积极开发相关设备,开展微波预处理污泥的连续和中试研究,推动微波技术在污泥资源化、减量化和无害化处理中的应用。

预处理对造纸污泥厌氧消化产甲烷性能的影响研究

采用碱(NaOH)和生物(蘑菇渣、绿色木霉)2种方法分别预处理造纸污泥,并将预处理后的造纸污泥与味精废液进行联合厌氧消化,研究不同预处理方式对造纸污泥的影响以及对后续联合厌氧消化甲烷产率的影响.结果表明,造纸污泥经过碱(NaOH)预处理和生物预处理(蘑菇渣、绿色木霉)后,污泥颗粒的结构变得紧实、平滑,颗粒间的孔隙度减少,污泥絮体中的纤维长度明显变短、污泥中的SCOD增加了35.5%～1130%、VSS降低了6%～19%、SVsludge增加了32%～192%,NH3-N浓度提高了36%～62.4%,表明预处理后污泥中的大分子物质被降解成小分子物质,且碱预处理对污泥产生的变化较生物处理大;经预处理后的造纸污泥与味精废液联合厌氧消化,甲烷得率分别为:NaOH预处理0.32m3CH4/kgVS、蘑菇渣预处理0.23m3CH4/kgVS,较CK分别提高了54%～88%和12%～34%,可见碱预处理提高甲烷产率效果更明显,由于蘑菇渣预处理具有成本低、解决二次污染、实现废物再利用等优点,因此两者在预处理提高造纸污泥厌氧消化甲烷产率方面都具有重要意义.

不同预处理方法对剩余污泥厌氧消化产沼气过程的影响

研究了不同预处理方法对剩余污泥固态法厌氧消化产沼气过程的影响。结果表明:不同的预处理方法均可不同程度地提高产气量和甲烷含量。其中,经酶法处理后,剩余污泥前4 h产气速率最快,平均每小时为3.29 mL/g;经热处理后,剩余污泥累积产气量最多,为45.80 mL/g,比对照提高了230%;而经微波处理后,剩余污泥所产沼气中甲烷质量分数最高,为62.26%,比对照增加了130%。

城市污水处理厂预热处理混合污泥的高温厌氧消化特性研究

针对165℃、30min预处理后的混合污泥,进行高温厌氧消化的连续试验.研究了在不同的水力停留时间（HRT）下的产气量、有机物的分解率等指标,探讨了“热处理＋高温消化”实用化的可行性.结果表明,总固体（TS）为70g·L^-1、预热处理后的混合污泥经高温厌氧消化,在HRT.为10、20、30d的条件下,产气率为2.82、1.70和1.19 L·L^-1·d^-1;降解单位COD的产气量为968、1053和1091 L·kg^-1;COD分解率为47%～52%;有机物分解率与HRT的关系符合一级反应动力学关系.COD物质平衡计算结果表明,基质中50%的固态有机物被分解转化,生物气中的甲烷含量可达59.1%.本研究中的厌氧消化反应可归纳为C8.38H19.7O7.59N＋3.86H2O→4.38CH4＋2.99CO2＋NH4^＋ ＋HCO3ˉ.

剩余污泥超声强化预处理及其厌氧消化效果

采用超声预处理方法破解剩余污泥,考查污泥理化性质的变化以及后续厌氧消化的性能。在3种不同超声波电功率密度下破解污泥,并对超声波电功率密度1.5W/mL、超声30min处理后的污泥进行厌氧消化实验,结果表明:污泥溶解性COD随着超声时间和超声波电功率密度的增加而线性上升.当超声波电功率密度分别为0.8和1.5W/mL、作用30min后,污泥溶解性COD是原泥的4.7倍和6.0倍.超声后污泥的pH值和碱度均有下降,同时污泥溶液的颗粒尺寸减小.超声污泥经厌氧消化后总COD去除率较对照组上升了13.5%.在5%污泥投配率下,超声组反应器在10d内即达到稳定产气状态,超声污泥的平均日产气量提高了57.9%.

低温短时热水解对剩余污泥厌氧消化的影响

研究了70～120℃,20min热水解预处理对剩余污泥有机物溶出、重金属释放及厌氧消化的影响.试验结果表明,化学需氧量、碳水化合物、蛋白质、DNA及氨氮(NH4—N)等指标的溶出在110℃以下都随着温度增加而增加,且在90～100℃之间有显著跳跃性增长,在120℃反而有所下降.污泥中微生物细胞在100℃时破裂.通过研究挥发性固体(VS)去除率和沼气产率来表征低温热水解对厌氧消化的影响,这2项指标均在110℃取得最大值.在上述研究基础上进行了相关性分析及回归分析,结果表明,所有的有机物溶出指标及厌氧消化性能均与预处理温度有显著的相关性,而单位降解VS产气与碳水化合物及蛋白质的溶出率呈很好的多元线性关系.

低频超声波预处理污泥的实验研究

污泥水解是污泥厌氧消化过程中的限速步骤,为提高污泥厌氧消化效率,采用低频超声波技术对污泥进行预处理,考察超声波作用时间以及声能密度对污泥预处理效果的影响。结果表明,低频超声波预处理可分散污泥絮体,使污泥内有机物大量溶出,提高污泥的厌氧消化性能。延长超声波作用时间或增加声能密度均有助于污泥中有机物、氮、磷等物质的释放。当超声波声能密度为0.138 W/mL时,超声波作用20min后,上清液溶解性COD(SCOD)、TN、TP分别为初始的11.7、4.1、9.9倍。挥发酸(VFA)的增加量取决于超声波频率,低频超声波对VFA无显著影响。超声波预处理对污泥絮体有很强的破碎作用,使胞外聚合物(EPS)溶解释放,当声能密度为0.034、0.069、0.138 W/mL时,超声波作用20min后,污泥上清液中的蛋白质质量浓度由初始的28.3mg/L分别增加到79.4、108.7、142.9mg/L;糖类质量浓度由初始的41.2mg/L增加到142.7、175.8、240.4mg/L。

γ-射线预处理对改善污泥厌氧消化特性的影响研究

采用γ-射线辐照法对污泥进行前处理,并对其主要厌氧消化性能指标进行对比分析研究。结果表明:污泥经γ-射线前处理后,能明显改善污泥的厌氧消化性能,并提高了污泥的厌氧消化速率。