Real-time control of aerobic/anoxic digestion for waste activated sludge

Experiments were conducted to study the performance characters of aerobic/anoxic （A/ A） digestion of sludge at 30± 1 ℃, while the sludge retention time （SRT） was kept 16 d. The varia tions of oxidation reduction potential （Eh ） and pH were continuously monitored during the A/A di gestion and the conversions of ammonium and nitrate were investigated. Important features on both Eh and pH profiles were identified to develop process control strategy. Since the feature point on Eh profile where d2 Eh/dt^2 =0 is very stable during anoxic cycle, it can be used to determine the end of denitrification. The end of nitrification can be identified according to dpH/dt = 0. A real-time control strategy of A/A digestion of sludge was developed and tested with pH and Eh as control parameters. It is shown that the performance of the real-time control strategy is better than that of a fixed time control strategy. While the real time controlled A/A digestion system can achieve a similar volatile suspended solids （VSS） destruction efficiency of 35.2 % as a continuously aerated system, it im proves the supernatant quality in a shorter aeration time（7. 75 d for a 20 d period）.

Combined alkaline and ultrasonic pretreatment of sludge before aerobic digestion

Alkaline and ultrasonic sludge disintegration can be used as the pretreatment of waste activated sludge （WAS） to promote the subsequent anaerobic or aerobic digestion. In this study, different combinations of these two methods were investigated. The evaluation was based on the quantity of soluble chemical oxygen demand （SCOD） in the pretreated sludge as well as the degradation of organic matter in the subsequent aerobic digestion. For WAS samples with combined pretreatment, the released COD levels were higher than those with ultrasonic or alkaline pretreatment alone. When combined with the ultrasonic treatment, NaOH treatment was more efficient than Ca（OH）2 for WAS solubilization. The COD levels released in various sequential options of combined NaOH and ultrasonic treatments were in the the following descending order： simultaneous treatment 〉 NaOH treatment followed by ultrasonic treatment 〉 ultrasonic treatment followed by NaOH treatment. For simultaneous treatment, low NaOH dosage （100 g/kg dry solid）, short duration （30 min） of NaOH treatment, and low ultrasonic specific energy （7500 kJ/kg dry solid） were suitable for sludge disintegration. Using combined NaOH and ultrasonic pretreatment with optimal parameters, the degradation efficiency of organic matter was increased from 38.0% to 50.7%, which is much higher than that with ultrasonic （42.5%） or with NaOH pretreatment （43.5%） in the subsequent aerobic digestion at the same retention time.

Autoheated thermophilic aerobic sludge digestion and metal bioleaching in a two-stage reactor system

A two-stage process has been developed for stabilization of sludge and removal of heavy metals from the secondary activated sludge with high rate of energy and time conservation. The first stage of the process involves autoheated thermophilic aerobic digestion at 55-60℃ inoculated with less-acidophilic thermophilic sulfur-oxidizing microorganisms （ATAD）. The results show that it is possible to maintain the autoheated conditions （55-60℃） in the ATAD reactor up to 24 hr, leading to reduction of 21% total solids （TS）, 27% volatile solids （VS）, 27% suspended solids （SS） and 33% volatile suspended solids （VSS） from the sludge. The sludge pH also decreased from 7 to 4.6 due to the activity of less-acidophilic thermophilic microorganisms. In the second stage operation, the digested sludge （pH 4.6, TS 31.6 g/L） from stage one was subjected to bioleaching in a continuous stirred tank reactor, operated at mean hydraulic retention times （HRTs） of 12, 24 and 36 hr at 30℃. An HRT of 24 hr was found to be sufficient for removal of 70% Cu, 70% Mn, 75% Ni, and 80% Zn from the sludge. In all, 39% VSS, 76% Cu, 78.2% Mn, 79.5% Ni and 84.2% Zn were removed from the sludge in both the stages.

Enhancing excess sludge aerobic digestion with low intensity ultrasound

In order to enhance the efficiency of aerobic digestion, the excess sludge was irradiated by low intensity ultrasound at a frequency of 28 kHz and acoustic intensity of 0.53 W/cm^2. The results show that the sludge stabilization without ultrasonic treatment can be achieved after 17 d of digestion, whereas the digestion time of ultrasonic groups can be cut by 3-7 d. During the same digestion elapsing, in ultrasonic groups the total volatile suspended solid removal rate is higher than that in the control group. The kinetics of aerobic digestion of excess sludge with ultrasound can also be described with first-order reaction.

Biodegradation Kinetics for Pre-treatment of Klebsiella pneumoniae Waste with Autothermal Thermophilic Aerobic Digestion

Biodegradation parameters and kinetic characteristics for pre-treating waste strains of Klebsiella pneu-moniae were studied in laboratory scale with an insulated reactor by an innovative technique,autothermal thermo-philic aerobic digestion(ATAD) . Based on an Arrhenius-type equation,an empirical model was developed to corre-late the removal of total suspended solid(TSS) with the initial TSS concentration,influent reaction temperature,aeration rate and stirring rate. The reaction temperatures of the ATAD system could be raised from the ambient temperatures of 25 °C to a maximum temperature of 65 °C. The exponentials for the initial TSS concentration,aeration rate and stirring rate were 1.579,-0.8175 and-0.6549,respectively,and the apparent activation energy was 6.8774 kJ·mol-1. The correlation coefficient for the pre-exponential factor was 0.9223. The TSS removal effi-ciency predicted by the model was validated with an actual test,showing a maximum relative deviation of 10.79%. The new model has a good practicability.

Kinetics model of aerobic phase in hybrid anoxic-oxic process

Kinetics models of COD degradation,biomass growth of the anoxic-oxic ( A/O) system as well as NH3-N degradation in aerobic phase were presented according to the mass balance theory,reaction-diffusion theory and Fick law. Then these models were testified by comparson with experimental results. It is demonstrated that the variation trends of theoretical and experimental values for COD degradation and biomass growth are similar. The deviation rate between theoretical and experimental values is always under 20% even it increases along with the fluctuation of influent organic loading. In terms of NH3-N degradation,nitrification can also be well simulated by the model as the substrates of influent are sufficient. It indicates that the model can accurately reflect the reaction in hybrid A/O process. Models presented herein provide a theoretical basis for the design, operation and control of hybrid A/O process.

Effect of lactic acid bacteria and propionic acid on conservation characteristics,aerobic stability and in vitro gas production kinetics and digestibility of whole-crop corn based total mixed ration silage

This study was conducted to evaluate the effect of lactic acid bacteria and propionic acid on the fermentation quality, aer- obic stability and in vitro gas production kinetics and digestibility of whole-crop corn based totalmixed ration （TMR） silage. Total mixed ration was ensiled with four treatments： （1） no additives （control）; （2） an inoculant （Lactobacillus plantarum） （L）; （3） propionicacid （P）; （4） propionic acid＋lactic acid bacteria （PL）. All treatments were ensiled in laboratory-scale silos for 45 days, and then subjected to an aerobic stability test for12 days. Further, four TMR silages were incubated in vitro with buffered rumen fluid to study in vitro gas production kinetics and digestibility. The results indicated that all TMR silages had good fermentation characteristics with low pH （〈3.80） and ammonia nitrogen （NH3-N） contents, and high lactic acid contents as well as Flieg points. Addition of L further improved TMR silage quality with more lactic acid production. Addition of P and PL decreased lactic acid and NH3-N contents of TMR silage compared to the control （P〈0.05）. After 12 days aerobic exposure, P and PL silages remained stable, but L and the control silages deteriorated as indicated by a reduction in lactic acid and an increase in pH, and numbers of yeast. Compared to the control, addition of L had no effects on TMR silage in terms of 72 h cumulative gas production, in vitro dry matter digestibility, metabolizable energy, net energy for lactation and short chain fatty acids, whereas addition of PL significantly （P〈0.05） increased them. L silage had higher （P〈0.05） in vitro neutral detergent fiber digestibility than the control silage. The results of our study suggested that TMR silage prepared with whole-crop corn can be well preserved with or without additives. Furthermore, the findings of this study suggested that propionic acid is compatible with lactic acid bacteria inoculants, and when used together, although they reduced lactic acid production of TMR silage, they improved aerobic stability and in vitro nutrients digestibility of TMR silage.

Removal of nitrogen and phosphorus in a combined A^2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.

Aerobic N_2O emission for activated sludge acclimated under different aeration rates in the multiple anoxic and aerobic process

Nitrous oxide（N_2O） is a potent greenhouse gas that can be emitted during biological nitrogen removal. N_2O emission was examined in a multiple anoxic and aerobic process at the aeration rates of 600 m L/min sequencing batch reactor（SBRL） and 1200 m L/min（SBRH）.The nitrogen removal percentage was 89% in SBRLand 71% in SBRH, respectively. N_2O emission mainly occurred during the aerobic phase, and the N_2O emission factor was 10.1%in SBRLand 2.3% in SBRH, respectively. In all batch experiments, the N_2O emission potential was high in SBRLcompared with SBRH. In SBRL, with increasing aeration rates, the N_2O emission factor decreased during nitrification, while it increased during denitrification and simultaneous nitrification and denitrification（SND）. By contrast, in SBRHthe N_2O emission factor during nitrification, denitrification and SND was relatively low and changed little with increasing aeration rates. The microbial competition affected the N_2O emission during biological nitrogen removal.

A novel multistage anoxic/aerobic process with sludge regeneration zone (R-MAO) for advanced nitrogen removal from domestic sewage

To achieve advanced nitrogen removal from actual municipal sewage,a novel multistage anoxic/aerobic process with sludge regeneration zone(R-MAO)was developed.The reactor was used to treat actual domestic sewage and the nitrogen removal capacity of the sludge regeneration zone(R zone)was investigated during the long-term operation.The best performance was obtained at the R zone’s Oxidation-Reduction Potential(ORP)of-50±30 mV and hydraulic residence times(HRT)of 1.2 hr.The average effluent COD,TN,NH_(4)^(+)-N and NO_(3)^(−)-N of the R-MAO process were 18.0±2.3,7.5±0.6,1.0±0.5 and 4.6±0.4 mg/L,respectively,with the corresponding removal efficiency of COD,TN and NH_(4)^(+)-N were 92.9%±1.0%,84.1%±1.5% and 97.5%±1.1%.Compared to the sole MAO system,the TN removal efficiency of the R-MAO increased by 10.1%.Besides,under the optimal conditions,the contribution of the R zone in the R-MAO that removal COD,TN,NH_(4)^(+)-N and NO_(3)^(−)-N were 0.36,0.15,0.032 and 0.82 g/day.High-throughput sequencing results showed that uncultured_bacterium_f_Burkholderiaceae(5.20%),OLB8(1.04%)and Ottowia(1.03%)played an important role in denitrification in the R zone.This study provided effective guidance for the design and operation of the R-MAO process in domestic sewage treatment.

Biopesticide production using Bacillus thuringiensis kurstaki by valorization of starch industry wastewater and effluent from aerobic,anaerobic digestion

Introduction Unconventional alternatives such as aerobic and anaerobic effluent from starch industry contain essential nutrients for Btk active ingredient synthesis.Effluent from starch industry is rich in carbon and nitrogen and can replace expensive feedstock used during the fermentation process.Objectives The main objective of this study was to achieve a biopesticide formulation from starch industry wastewater(SIW)with high entomotoxicity(UI/ml)of larvae comparable to Foray 76B,which is a commercial biopesticide.Methods Bacillus thuringiensis var kurstaki HD1(Btk)strain was cultivated and sub-cultured to aerobic,anaerobic digested effluent and SIW.Pre-treatment was carried on these different substrates to enhance the residual carbon required for Btk growth and delta endotoxin synthesis.After 48 hours of fermentation,cells count and delta-endotoxin were determined.A biopesticide formulation containing fermented broth and adjuvants was fed to larvae to determine larvae mortality.Results Btk cell growth and sporulation profile in SIW media displayed a high total cell count and viable spores compared to btk growth in anaerobic or aerobic media after 48h fermentation.The maximum endotoxin concentration in the SIW medium was 435μg/mL,whereas,in anaerobic and aerobic effluent,the maximum concentrations were at 161μg/mL and 136μg/mL,respectively.When acidic treatment was performed at pH 2 for these substrates,entomotoxicity obtained from aerobic and anaerobic biopesticide formulations displayed significantly higher entomoxicity than the untreated ones.The entomotoxicity of SIW treated at pH 2 was equivalent to the standard Foray 76B which is 20,000 IU/μL.Conclusion Anaerobic and aerobic effluent did not contain enough total organic carbon to augment Btk growth and entomo-toxicity.Substrates pre-treated at pH 2 provided significant organic matter for Btk growth and resulted in larval mortality equivalent to the com ercial biopesticide Foray 76B.

Effect of nitrate concentration on filamentous bulking under low level of dissolved oxygen in an airlift inner circular anoxic-aerobic incorporate reactor

This laboratory research investigated a possible cause of filamentous bulking under low level of dissolved oxygen conditions （dissolved oxygen value in aerobic zone maintained between 0.6-0.8 mgO2 /L） in an airlift inner-circular anoxic-aerobic reactor. During the operating period, it was observed that low nitrate concentrations affected sludge volume index significantly. Unlike the existing hypothesis, the batch tests indicated that filamentous bacteria （mainly Thiothrix sp.） could store nitrate temporarily under carbon restricted conditions. When nitrate concentration was below 4 mg/L, low levels of carbon substrates and dissolved oxygen in the aerobic zone stimulated the nitrate-storing capacity of filaments. When filamentous bacteria riched in nitrate reached the anoxic zone, where they were exposed to high levels of carbon but limited nitrate, they underwent denitrification. However, when nonfilamentous bacteria were exposed to similar conditions, denitrification was restrained due to their intrinsic nitrate limitation. Hence, in order to avoid filamentous bulking, the nitrate concentration in the return sludge （from aerobic zone to the anoxic zone） should be above 4 mg/L, or alternatively, the nitrate load in the anoxic zone should be kept at levels above 2.7 mg NO-3N/g SS.

Effects of anaerobic digestion and aerobic treatment on the reduction of gaseous emissions from dairy manure storages

Effects of anaerobic digestion and aerobic treatment on the reduction of gaseous emissions from dairy manure storages were evaluated in this study.Screened dairy manure containing 3.5%volatile solids(VS)was either anaerobically digested or aerobically treated prior to storage in air-tight vessels.Anaerobic digestion was carried out using a mesophilic anaerobic sequencing batch reactor operated at a hydraulic retention time of 20 days and an organic loading rate(OLR)of 1 gVS/L/day.Aerobic treatment was achieved using an aerobic reactor operated at a hydraulic retention time(HRT)of 10 days and an OLR of 2 gVS/(L·d).The treated manure was put into the storage on a daily basis for a period of 180 days.All the gases produced during this period were captured and analyzed for methane,carbon dioxide and volatile organic compounds(VOCs).Untreated manure was stored and analyzed in the same way as the treated manure and used as a control for comparison.The results show that low amounts of gases were produced during the first 84 days of storage in both treated and untreated manure,but increased significantly after this time point.The generally expected positive impacts of anaerobic and aerobic treatment on the reductions of methane and VOCs were confirmed in this study.However,the effects of anaerobic and aerobic treatment varied over the time of storage,especially for VOCs.The results of this study indicate that to achieve significant reductions in VOC emission the storage time of anaerobic digester or aerobic reactor effluent should be limited to no more than 100 days.

厨余垃圾处理技术现状与发展趋势分析

文章在技术现状分析中,对比了现有厨余垃圾处理处置路线,认为肥料化土地利用是未来的优先选项。厨余垃圾处理方式主要包括协同处理、分质处理、定制化处理处置、分散处理与集中处理相结合;技术主要包括厨余垃圾全量化处置利用途径、厨余垃圾高效分质除杂预处理技术及装备、厨余垃圾有机组分精细化利用及全量化消纳技术、惰性及毒害组分无害化处置技术。

城市餐厨垃圾资源化处理的研究进展

城市餐厨垃圾逐年增加,产生量大,组成复杂,同时含有丰富的有机物、蛋白质和油脂等,具有非常广阔的资源化利用前景。传统的餐厨垃圾处理方式对生态环境和居民健康构成潜在威胁,已不适应当前的发展环境。无害化、减量化和资源化是未来餐厨垃圾处置的发展方向。结合餐厨垃圾的组成与特性,分析传统处理方式,并综述餐厨垃圾资源化处理技术的研究进展,以更好地实现资源化利用。

一体化厌氧-变级数缺氧/好氧循环流污水处理装置中试研究

针对现有村镇污水处理技术与装备的不足,开发出适用于村镇污水处理的新型一体化厌氧-变级数缺氧/好氧循环流(A-(AO)_n)同步脱氮除磷、沉淀分离技术与装备,以长沙某污水提升泵站沉砂池的出水作为处理对象开展中试实验。对好氧区不同溶解氧、填料填充比和分区进水条件下装置污水处理效能的变化进行研究,结果表明:当好氧区溶解氧控制在1.5~2.0 mg/L,好氧区填料填充比为30%时,装置的脱氮除磷效果最佳。在不外加碳源且不投加化学除磷药剂的条件下,出水水质优于《城镇污水处理厂污染物排放标准》(GB 18918—2002)的一级A标准。高通量测序结果显示,好氧区投加悬浮球填料后,系统中微生物总量和多样性明显提高,为系统中发生同步硝化反硝化(SND)现象创造了条件。

品种和有机肥对全株玉米青贮品质、消化特性及有氧稳定性的影响

试验旨在探讨有机肥对不同品种的全株玉米青贮品质、消化特性及有氧稳定性的影响。采用双因素试验设计,选用大康205(DK205)、高油958(HO958)、中玉335(ZY335)和中农787(ZN787)4个玉米品种,分别进行施用有机肥和不施用有机肥两个处理,于蜡熟期收割并进行全株青贮,发酵200 d后对相关指标进行分析。结果表明,品种和有机肥的互作效应对乳酸、乙酸、丙酸、丁酸含量和氨态氮/总氮比值有影响(P<0.05);品种和有机肥的互作效应可影响干物质、粗蛋白、淀粉和酸性洗涤纤维含量(P<0.05)。施用有机肥组的体外干物质消化率及有氧稳定性较高,中农787的体外中性洗涤纤维消化率高于其他3个品种(P<0.05)。研究表明,施用有机肥对不同品种全株玉米青贮品质、消化特性及有氧稳定性均起到不同程度的改善作用,中农787适宜作为全株青贮玉米品种在内蒙古地区推广种植,施用有机肥可以进一步提高青贮品质。

鼠李糖脂对污泥自热高温微氧体系有机碳源释放的影响

为探究表面活性剂在自热高温微氧(ATMAD)发酵体系中对有机碳源的释放会产生何种影响,选取鼠李糖脂(RL)这一无毒无害且易于获取的典型生物表面活性剂,依托ATMAD发酵体系,展开实验探究.结果表明,投加0.02~0.07g/gTSS鼠李糖脂对反应体系中污泥的溶解,可溶性有机物的释放及挥发性脂肪酸的积累有较为明显的促进作用,相关指标均有明显提高,产酸相关功能菌的丰度也有所增加,当投加量为0.07g/gTSS时,VFA累积浓度最高,为空白组的1.63倍,判断此时为最佳投放浓度;当投加浓度高于0.10g/gTSS时,会对有机碳源的释放产生抑制.在ATMAD体系中添加适量鼠李糖脂对于开发优质外加碳源这一工作具有较高的可行性.

填料-厌氧-好氧消化+复合酶工艺对城市污水处理及污泥减量的效能

针对当前城市污水处理要求不断提高,以及污水处理工艺产生大量污泥给后续污泥处理处置带来的困难,研究旨在开发一种污泥减量技术,既能降低污泥产率,又能保证污泥沉降性能,同时保障污水处理效果。通过对比运行试验,研究了在恒温条件下好氧-沉淀-厌氧(OSA)工艺和填料-厌氧-好氧消化工艺分别在加入与不加入高效溶胞复合酶处理下的污泥减量效果,以及对污泥上清液有机物和营养盐类的去除效能。结果表明,消化工艺经过6 d后,填料-厌氧-好氧消化+复合酶工艺的污泥降低率可达到44.0%,污泥减量效果最佳。此外,该工艺能使溶解性化学需氧量(SCOD_(Cr))维持在180~200 mg/L,pH值维持在6.8~7.0,氨氮维持在3~4 mg/L,NO_(3)^(-)-N维持在36~43 mg/L,从而保证出水水质。同时污泥容积指数(SVI)无明显变化,确保了污泥沉降性能。

厌氧消化和好氧堆肥对城市污泥中新污染物的削减

城镇污水处理规模的扩大使得城市污泥的产生量增加,而药物及个人护理品(PPCPs)、生物性污染物、微塑料(MPs)和雌激素等新污染物在污泥中的检出率也呈增加趋势。污泥厌氧消化制沼气、好氧堆肥制土壤改良剂具有削减污染物、回收有价值组分、降低环境风险等多重功效,然而它们对新污染物的削减效果尚待考察。以上述4种新污染物为例,比较了它们在不同国家城市污泥中的存在状况,综述了厌氧消化、好氧堆肥、厌氧消化和好氧堆肥结合以及与物化措施联合对新污染物的削减情况及存在的问题。针对污泥中多种新污染物并存的状况,提出未来应开发针对多种新污染物的去除技术,同时强化新污染物削减机制的研究,以保障城市污泥的安全利用。