Operating strategies for acid phase digestion: an industrial case study

Acid phase digestion was investigated for enhanced operation in an industrial wastewater treatment plant. In particular, sludge retention time (SRT), temperature and pH were assessed for determining optimal conditions under operating constraints. Volatile fatty acid (VFA) production and soluble chemical oxygen demand (SCOD) were the key process parameters used to assess system performance. Increase in SRT from 0.8 to 1.4 days (at 22°C) had moderate effect on VFA production (approximately 15% increase), achieving a maximum VFA production of 3600 mg/L. High VFA production rate (0.101 ± 0.035 mg/mgVS.d) was obtained at the highest operating retention time during summer (27°C). The degree of solubilisation of particulate organic matter increased with temperature and retention time. Despite an increase in SCOD (6472 ± 873 mg/L max.), a corresponding increase in VFA was not observed. SCOD showed a linear correlation with decrease in pH, while acidogenesis (SCOD conversion to VFA) was found to be favourable at a pH of 4.5.     

SDS和SDBS强化污泥水解的实验研究

在污泥中投加2种表面活性剂SDS和SDBS进行预处理,从COD溶出率、溶解性糖类和蛋白质3个方面对预处理后污泥的性质进行了研究。结果表明,二者的加入极大地促进了污泥的水解,低剂量范围时SCOD随投加剂量增加而显著升高,投加剂量在50 mg/g dw以上时SCOD增幅不明显。SCOD分别由初始时的638.5 mg/L最高上升到6 446.8 mg/L(SDBS)和4 857.2 mg/L(SDS),溶出率分别由初始时的5.8%最高上升到37.3%(SDBS)和30.2%(SDS)。在0~150 mg/g dw剂量范围内,溶解性糖类和蛋白质随两者投加剂量增加呈线性升高趋势,溶解性糖类分别由初始时的3.54 mg/L最高上升到95.56 mg/L(SDBS)和64.20 mg/L(SDS)。溶解性蛋白质分别由初始时的11.72 mg/L最高上升到706.30 mg/L（SDBS）和541.08 mg/L（SDS）。氨氮和VFA浓度也随投加量升高,氨氮浓度分别由初始时的4.21 mg/L最高上升到130.33 mg/L(SDBS)和102.74 mg/L(SDS);VFA浓度分别由初始时的21.27 mg/L最高上升到358.30 mg/L(SDBS)和283.12 mg/L(SDS)。     

水解酸化池预处理低碳生活污水的效能分析

为了提高低碳氮比生活污水的脱氮效能,在缺氧池前设置水解酸化池,通过水解酸化作用改善进水碳源,同时对回流剩余污泥进行降解,以期达到改善进水碳源可生化性、提高其可利用率、减少外碳源投加量并实现污泥减量的目的。分别考察了水解酸化池对污水单独进行预处理以及对污水和回流污泥同时进行预处理情况下的作用效能及其对系统脱氮的影响。结果表明:两种预处理条件下,理论B/C值都大于0.65,出水SCOD/COD的平均值和出水VFA浓度均高于进水,单独污水水解酸化的出水SCOD减少较多,对TN的去除率仅为47.8%;回流剩余污泥后,温度>20℃且每日分4次共回流20 L剩余污泥的TN去除效果明显优于单独污水水解酸化和温度<20℃且每日分2次共回流10 L的运行效果,两种回流量条件下对TN的去除率分别为71.9%和66.1%,污泥减量率分别为58%和56.3%。     

Effects of chromium (VI) addition on the activated sludge process

The effect of hexavalent chromium, Cr(VI), addition on various operating parameters of activated sludge process was evaluated. To accomplish this, two parallel lab-scale continuous-flow activated sludge plants were operated. One was used as a control plant, while the other received Cr(VI) concentrations equal to 0.5, 1, 3 and 5 mgl(-1). Cr(VI) concentrations of 0.5 mgl(-1) caused significant inhibition of the nitrification process (up to 74% decrease in ammonia removal efficiency). On the contrary, the effect of Cr(VI) on organic substrate removal was minor for concentrations up to 5 mgl(-1), indicating that heterotrophic microorganisms are less sensitive to Cr(VI) than nitrifiers. Activated sludge floc size and structure characterization showed that Cr(VI) concentrations higher than 1 mgl(-1) reduced the filaments abundance, causing the appearance of pin-point flocs and free-dispersed bacteria. Additionally, the variability of protozoa and rotifers was reduced. As a result of disperse growth, effluent quality deteriorated, since significant amounts of suspended solids escaped with the effluent. Termination of Cr(VI) addition led to a partial recovery of the nitrification process (up to 57% recovery). Similar recovery signs were not observed for activated sludge floc size and structure. Finally, shock loading to the control plant with 5 mgl(-1) Cr(VI) for 2 days resulted in a significant inhibition of the nitrification process and a reduction in filamentous microorganisms abundance.     

Enhanced hydrolysis of carbohydrates in primary sludge under biosulfidogenic conditions

The potential for using readily available and cost-effective complex carbon sources, such as primary sludge (PS), for the bioremediation of sulfate-rich effluent streams, including acid mine drainage, has been constrained by the slow rate of solubilization and low yield of soluble products. Disposal of PS also remains a global problem. Recent studies of a patented recycling sludge bed reactor have shown that the solubilization of PS is enhanced under biosulfidogenic conditions. The current study investigated the enhanced solubilization of the carbohydrate fraction of PS under these conditions, using selective metabolic inhibitors. The mean maximum rate of reducing sugar production was significantly higher under sulfidogenic (167 mg L(-1)h(-1)) than methanogenic (51 mg L(-1)h(-1)) conditions and the utilization of volatile fatty acids under sulfidogenic conditions was rapid. Analysis of VFA profiles indicated preferential utilization of longer chain acids under sulfidogenic conditions and of acetate in the methanogenic systems and that the acetogenic step was unlikely to be rate-limiting in the solubilization of complex carbon.     

Biological hydrolysis and acidification of sludge under anaerobic conditions: the effect of sludge type and origin on the production and composition of volatile fatty acids

New wastewater treatment processes resulting in considerably reduced sludge production and more effective treatment are needed. This is due to the more stringent legislations controlling discharges of wastewater treatment plants (WWTPs) and existing problems such as high sludge production. In this study, the feasibility of implementing biological hydrolysis and acidification process on different types of municipal sludge was investigated by batch and semi-continuous experiments. The municipal sludge originated from six major treatment plants located in Denmark were used. The results showed that fermentation of primary sludge produced the highest amount of volatile fatty acids (VFAs) and generated significantly higher COD- and VFA-yields compared to the other sludge types regardless of which WWTP the sludge originated from. Fermentation of activated and primary sludge resulted in 1.9-5.6% and 8.1-12.6% COD-yields, soluble COD (SCOD)/total COD (TCOD), in batch experiments, respectively. The COD-yields for primary, activated and mixed sludge were 19.1%, 6.5% and 21.37%, respectively, in semi-continuous experiments operated at solids retention time (SRT) of 5d and temperature of 37 degrees C. The benefit of fermentation for full-scale application was roughly estimated based on the experiments performed in semi-continuous reactors. The results revealed that even though the VFA production of primary sludge was higher compared to activated sludge, substantial amounts of VFA could be produced by fermentation of activated sludge due to the substantially higher production of activated sludge in WWTPs.     

Biodegradation and effect of formaldehyde and phenol on the denitrification process

Formaldehyde and phenol biodegradation during the denitrification process was studied at lab-scale, first in anoxic batch assays and then in a continuous anoxic reactor. The biodegradation of formaldehyde (260 mgl(-1)) as single carbon source and at phenol concentrations ranging from 30 to 580 mgl(-1) was investigated in batch assays, obtaining an initial biodegradation rate around 0.5g CH(2)OgVSS(-1)d(-1). With regard to phenol, its complete biodegradation was only observed at initial concentrations of 30 and 180 mgl(-1). The denitrification process was inhibited at phenol concentrations higher than 360 mgl(-1). Studies were also done using a continuous anoxic upflow sludge blanket reactor in which formaldehyde removal efficiencies above 99.5% were obtained at all the applied formaldehyde loading rates, between 0.89 and 0.14g COD (CH(2)O)l(-1)d(-1). The phenol loading rate was increased from 0.03 to 1.3g COD (C(6)H(6)O)l(-1)d(-1). Phenol removal efficiencies above 90.6% were obtained at phenol concentrations in the influent between 27 and 755 mgl(-1). However, when the phenol concentration was increased to 1010 mgl(-1), its removal efficiency decreased. Denitrification percentages around 98.4% were obtained with phenol concentrations in the influent up to 755 mgl(-1). After increasing phenol concentration to 1010 mgl(-1), the denitrification percentage decreased because of the inhibition caused by phenol.     

碱解预处理对污泥固体的破解及减量化效果

采用向污泥中加碱的预处理方式，考察了碱解预处理对污泥固体的破解及减量化效果。结果表明，污泥SCOD浓度随投碱量的增加而增加，在投碱量为1gNaOH／gTS的情况下，挥发性悬浮固体的分解率可达62．05％。碱解作用下，污泥的水解分为快速水解和慢速水解两个阶段，对两阶段水解过程的动力学分析结果表明，碱解预处理仅对第一阶段（快速水解过程）有显著促进作用，而对第二阶段（慢速水解过程）的作用则不明显。     

超声破解促进污泥两相厌氧消化性能研究

以频率为40kHz,声能密度为0．1、0．3和0．6W／mL的超声波对城市污水处理厂的剩余污泥进行超声破解,研究破解效应对污泥两相厌氧消化工艺去除有机物的效果、生物气产量和产气率的影响。结果表明,超声破解能显著提高污泥的溶解性COD（SCOD）浓度、对有机物的去除率、生物气产量和产气率,缩短两相厌氧消化工艺的污泥停留时间。污泥在声能密度为0．6w／mL的条件下破解60min后,SCOD从440mg／L提高到8844mg／L,COD的溶出率达到32．0％。对原污泥和经超声波破解60min的污泥进行两相厌氧消化试验,结果显示：经超声波破解后,对COD和总挥发性固体（VS）的去除率较原污泥分别提高了一半左右,产气量和产气率分别增长了125．3％和72．5％。     

Fermentation and elutriation of primary sludge: effect of SRT on process performance

A primary sludge fermentation-elutriation pilot plant was operated using in-line and side-stream schemes. The influence of solids retention time, recirculation sludge flow-rate and solids concentration on the fermentation-elutriation process performance has been assessed in this paper. The use of high elutriation flows (12% of influent flow) improved the volatile fatty acids (VFA) concentration in the effluent stream. Suspended solids removal efficiency decreased in the primary settler when the solids retention time (SRT) was increased from 4 to 8 days. Disintegration step during hydrolysis process was pointed out as the main reason for that decrease. Maximum VFA productions were achieved at SRT between 6 and 8 days at the highest elutriation flow tested for both configurations. Propionic, butyric and valeric volatile fatty acids percentage increased when total solids sludge concentrations above 23,000mgl(-1) were used. Hydrogen accumulation, causing acetogenic bacteria inhibition, was indicated as the reason for C(3)-C(5) fatty acids accumulation.     

Effects of temperature transient conditions on aerobic biological treatment of wastewater

The effects of temperature variations on aerobic biological wastewater treatment were evaluated with respect to treatment efficiency, solids discharges, sludge physicochemical properties and microbiology. The effects of controlled temperature shifts (from 35 degrees to 45 degrees C; from 45 degrees to 35 degrees C) and periodic temperature oscillations (from 31.5 degrees C to 40 degrees C, 6-day period, for 30 days) were assessed in 4 parallel, lab-scale sequencing batch reactors (SBRs) that treated pulp and paper mill effluent. Overall, the temperature shifts caused higher effluent suspended solids (ESS) levels (25-100 mg/L) and a decrease (up to 20%) in the removal efficiencies of soluble chemical oxygen demand (SCOD). Lower ESS levels were triggered by a slow (2 degrees C/day) versus a fast (10 degrees C/12h) temperature shift from 35 degrees to 45 degrees C, but the SCOD removal efficiencies decreased similarly in both cases (from 66+/-3% and 65+/-2% to 49+/-3% and 51+/-3%). Temperature oscillations caused an increased deterioration of the sludge settleability [high sludge volume indices (SVI); low zone settling velocities (ZSV)], high ESS levels and lower SCOD removals. The temperature transients were associated with poor sludge settleability (SVI>100 mL/g MLSS, ZSV<1 cm/min), more negatively charged sludge (up to -0.35+/-0.03 meq/g MLSS), increased filament abundance (approximately 4 to 4.5, subjective scale equivalent to very common), and decreased concentrations of protozoa and metazoa (25,000-50,000 microorganisms/mL sludge). The controlled, periodic temperature oscillations had a slight impact on SCOD removal efficiency (5% decrease), and did not seem to select for robust microorganisms that withstood the temperature shift. Sludge deflocculation and filament proliferation caused by these temperature transients may explain the higher ESS levels.     

Effect of operating parameters on molinate biodegradation

The effect of operating conditions during molinate degradation by the defined mixed bacterial culture DC, previously described as able to mineralize molinate, was evaluated in a batch reactor. Parameters such as the rate of molinate degradation, the dissolved organic carbon (DOC) consumption and the accumulation of molinate degradation products were monitored along the culture growth. The effect of conditions such as temperature, pH, aeration rate, salinity, and presence of additional carbon and/or nitrogen sources, was tested independently. Degradation of molinate in river water was also evaluated. Culture DC was able to grow and to mineralize molinate at all the conditions assayed. Temperature was the factor with the strongest influence on bacterial growth and molinate mineralization. The lowest and the highest rate values of growth (0.010 and 0.110 h(-1)) and of molinate degradation (0.027 and 0.180 g molinate g(-1)celldrywth(-1)) were obtained at 15 and 35 degrees C, respectively. In cultures with approximately 187 mgl(-1) of molinate, 2-oxo-molinate was the major molinate degradation product accumulated in the medium, in concentrations below 0.133 mgl(-1). Degradation of molinate was also evaluated in a continuous stirred tank reactor (CSTR). Operating the CSTR at a hydraulic retention time (HRT) of 83 h, fed with medium containing molinate concentrations ranging from 1 to 3mM, culture DC degraded the herbicide with specific degradation rates similar to those obtained in the batch systems.     

臭氧破解对剩余污泥性质的影响

通过不同臭氧投加量对剩余污泥的破解试验,系统地研究了臭氧破解过程中剩余污泥基质和上清液中相关指标的变化规律。试验结果表明,臭氧破解能够有效减少污泥中固体物质的含量,在臭氧投加量为250 mg/g(O3/TS)的条件下,总残渣(TS)和挥发性固体(VS)分别减少了31.33%和35.59%;臭氧破解使得污泥上清液中的溶解性化学需氧量(SCOD)、总氮、总磷、氨氮含量均明显上升,pH值则呈下降趋势,但降幅不大。     

Control of the sulfide (S2-) concentration for optimal zinc removal by sulfide precipitation in a continuously stirred tank reactor

Precipitation of Zn2+ with S2- was studied at room temperature in a continuously stirred tank reactor of 0.5l to which solutions of ZnSO4 (800-5800 mgl(-1) Zn2+) and Na2S were supplied. The pH was controlled at 6.5 and S2- concentration in the reactor was controlled at set point values ranging from 3.2x10(-19) to 3.2x10(-4) mgl(-1), making use of an ion-selective S2- electrode. In steady state, the mean particle size of the ZnS precipitate decreased linearly from 22 to 1 microm for S2- levels dropping from 3.2x10(-4) to 3.2x10(-18) mgl(-1). At 3.2x10(-11) mgl(-1) of S2-, the supplies of ZnSO4 and Na2S solutions were stoichiometric for ZnS precipitation. At this S2- level, removal of dissolved zinc was optimal with effluent zinc concentration <0.03 mgl(-1) while ZnS particles formed with a mean geometric diameter of about 10 microm. Below 3.2x10(-11) mgl(-1) of S2- insufficient sulfide was added for complete zinc precipitation. At S2- levels higher than 3.2x10(-11) mgl(-1) the effluent zinc concentration increased due to the formation of soluble zinc sulfide complexes as confirmed by chemical equilibrium model calculations.     

Modified ADM1 structure for modelling municipal primary sludge hydrolysis

This study elaborates the rate-limiting steps of particle disintegration/hydrolysis of primary sludge using methane production rate (MPR) curves from multiple batch experiments. Anaerobic batch degradation of fresh primary sludge showed a complex MPR curve marked with two well-defined temporal peaks. The first immediate peak was associated with the degradation of relatively readily hydrolysable substrates, while the second delayed peak was associated with the degradation of large-sized particles. For simulating the second delayed peak, it was necessary to consider a more elaborate particle disintegration/hydrolysis model. Based on the anaerobic respirograms of 17 runs in four datasets and using a substrate characterisation approach similar to activated sludge models (ASMs), the primary sludge was classified into three biodegradable fractions having different kinetics. These are (1) a hydrolysable substrate (X(Settle-I)) showing a degradation typical to slowly biodegradable compounds, (2) a substrate fraction (X(Settle-II)) having a degradation similar to lysis of biomass fraction and (3) a substrate requiring disintegration before hydrolysis (X(Settle-III)) representing the large-sized particles in primary sludge. Based on these results, modifications in the model structure of anaerobic digestion model no. 1 (ADM1) are proposed to improve the modelling of primary sludge solid degradation in anaerobic digesters.     

污泥超声预处理的影响因素分析

对污泥超声预处理技术的基础研究是实现该技术工程应用的前提，为此取深圳市某污水处理厂二沉池污泥和浓缩污泥进行超声破解试验。结果表明，污泥破解程度随着超声输入能量的增加而提高，而且低强度、长时间超声作用的效果好于高强度、短时间作用；温度升高有助于污泥破解，但随着温度升高幅度的增加其贡献下降；污泥含水率越高则COD的溶出率越高，但低含水率污泥的能量利用效率更高；搅动有利于污泥破解；污泥破解COD溶出率（DDCOD）与超声声能密度（E）和辐射时间（t）的关系可以用DDCOD=kE^mt^n表示，这为该技术的应用提供了理论支持。     

Evaluation of metal hydroxide sludge for reactive dye adsorption in a fixed-bed column system

The capacity and performance of small-scale column, containing coarse particles of metal hydroxide sludge, were evaluated using 30mgl(-1) dye solutions of C.I. Reactive Red 141. The studied bed depths were 2.5-20cm and the studied flow rates were 1.1, 2.2 and 3.3mlmin(-1)cm(-2). At the breakthrough point of 0.1C(t)/C(0), the breakthrough volume was increased with increasing bed depth or decreasing flow rate, due to an increase in empty bed contact time (EBCT). The data followed the bed depth service time model, and the adsorption capacity was 24-26mgcm(-3) or 27-29mgdyesg(-1) adsorbent. The minimum bed depths should be higher 1.02, 2.04 and 2.59cm with flow rates of 1.1, 2.2 and 3.3mlmin(-1)cm(-2), respectively, while the ratio of bed depth to diameter should not be higher than 6. With EBCT above 5min, the usage rate of metal hydroxide sludge was 1.3gl(-1). Using the bed depth of 5cm and the flow rate of 0.55mlmin(-1)cm(-2), 87% of dominant colour, 78% of COD, and 99% of SS could be removed from the textile wastewater, and the leachate of toxic heavy metals was under the standard limitations.     

Stability of the bacterial communities supported by a seven-stage biological process treating pharmaceutical wastewater as revealed by PCR-DGGE

The stabilities of the bacterial community structures supported by seven full-scale biological reactors treating pharmaceutical wastewater were investigated by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplified 16S rRNA gene fragments. Effluent quality from this treatment process was consistently high with respect to BOD5 (<30 mgl(-1)), soluble COD (<500 mgl(-1)), and total ammonia (< 5 mgl(-1) as N) concentrations. Long-term community structure stability was studied by comparing the similarity of PCR-DGGE fingerprints from samples collected 87 days apart between which the influent wastewater characteristics were relatively stable. The Dice index (Cs) of similarity was moderately high for the first four reactors (Cs = 0.61-0.77) and very high for the last three reactors (Cs = 0.89-0.91). Short-term community structure stability was studied by comparing PCR-DGGE fingerprints from samples collected 15 days apart between which the influent wastewater characteristics changed significantly, while the effluent quality remained consistently high. The bacterial community composition of each of the seven bioreactors showed a moderate community shift (Cs = 0.70-0.76). Short-term variability in influent wastewater composition, therefore, affected a greater community shift than did long-term operation treating a wastewater of relatively consistent composition. These results indicate that functionally stable wastewater treatment bioreactors have stable microbial community structures under normal operating conditions but are able to adapt in response to perturbations to sustain high effluent quality.     

Aerobic moving bed biofilm reactor treating thermomechanical pulping whitewater under thermophilic conditions

The continuously operated laboratory scale Kaldnes moving bed biofilm reactor (MBBR) was used for thermophilic (55 degrees C) aerobic treatment of TMP whitewater. In the MBBR, the biomass is grown on carrier elements that move along with the water in the reactor. Inoculation with mesophilic activated sludge gave 60-65% SCOD removal from the first day onwards. During the 107 days of experiment, the 60-65% SCOD removals were achieved at organic loading rates of 2.5-3.5 kg SCODm(-3) d(-1), the highest loading rates applied during the run and HRT of 13-22h. Carbohydrates, which contributed to 50-60% of the influent SCOD. were removed by 90-95%, while less than 15% of the lignin-like material (30-35% of SCODin) was removed. The sludge yield was 0.23g VSSg SCOD(-1)removed. The results show that the aerobic biofilm process can be successfully operated under thermophilic conditions.     

NOx monitoring of a simultaneous nitrifying-denitrifying (SND) activated sludge plant at different oxidation reduction potentials

Simultaneous nitrification-denitrification (SND) allows biological nitrogen removal in a single reactor without separation of the two processes in time or space but requires adapted control strategies (anoxic/aerobic conditions). In this study, the formation of gaseous nitric oxide (NO(G)) and nitrogen dioxide (NO(2G)) was monitored for SND in relation to the oxidation-reduction potential (ORP) and nitrogen removal in a lab batch reactor and a pilot membrane bio-reactor (MBR). In addition hospital wastewater (COD/N(tot)>6:1) was treated on site for 1 year. The highest total nitrogen removal rates of max 90% were reached at 220-240mV ORP (given as E(h)) with corresponding maximal NO(G) emissions rates of 0.9microgg(-1)VSSh(-1). The maximal emission rates of NO(2G) (0.2microgg(-1)VSSh(-1)) were reached at the same ORP level and the NO(2G) emissions correlated to the nitrite accumulation in the activated sludge up to 5mgl(-1)NO(2L)-N. It was shown that this correlation was due to biological production and not due to pH-dependent chemical conversion. Therefore, NO(2G) can be used as additional control loop for ORP-controlled SND systems to avoid the inhibition of denitrification and high nitrite concentrations in the plant effluent.