Treatment of paper mill effluent using an anaerobic/aerobic hybrid side-stream membrane bioreactor

This paper presents the design and operational performance data of an anaerobic/aerobic hybrid side-stream Membrane Bioreactor (MBR) process for treating paper mill effluent operated over a 6 month period. The paper mill effluent stream was characterized by a chemical oxygen demand (COD) range of between 1,600 and 4,400 mg/L and an average BOD of 2,400 mg/L. Despite large fluctuations in COD feed concentration, stable process performance was achieved. The anaerobic Expanded Granular Sludge Bed (EGSB) pre-treatment step effectively lowered the organic loading by 65 to 85%, thus lowering the MBR COD feed concentration to consistently below 750 mg/L. The overall MBR COD removal was consistent at an average of 96%, regardless of the effluent COD or changes in the hydraulic retention time (HRT) and organic loading rate (OLR). Combining a high-rate anaerobic pre-treatment EGSB with a Modified Ludzack-Ettinger (MLE) MBR process configuration produced a high quality permeate. Preliminary NF and RO results indicated an overall COD removal of around 97 and 98%, respectively.     

Treatment of low and medium strength sewage in a lab-scale gradual concentric chambers (GCC) reactor.

One of the major challenges of anaerobic technology is its applicability for low strength wastewaters, such as sewage. The lab-scale design and performance of a novel Gradual Concentric Chambers (GCC) reactor treating low (165+/-24 mg COD/L) and medium strength (550 mg COD/L) domestic wastewaters were studied. Experimental data were collected to evaluate the influence of chemical oxygen demand (COD) concentrations in the influent and the hydraulic retention time (HRT) on the performance of the GCC reactor. Two reactors (R1 and R2), integrating anaerobic and aerobic processes, were studied at ambient (26 degrees C) and mesophilic (35 degrees C) temperature, respectively. The highest COD removal efficiency (94%) was obtained when treating medium strength wastewater at an organic loading rate (OLR) of 1.9 g COD/L.d (HRT = 4 h). The COD levels in the final effluent were around 36 mg/L. For the low strength domestic wastewater, a highest removal efficiency of 85% was observed, producing a final effluent with 22 mg COD/L. Changes in the nutrient concentration levels were followed for both reactors.     

Effects of nitrobenzene concentrations and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor and continuously stirred tank reactor system.

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention time (HRT) on the performance of anaerobic baffled reactor (ABR) and aerobic completely stirred tank reactor (CSTR) were studied. In the first step the NB concentration was increased from 30 to 700 mg/L at constant COD and flowrates. Maximum COD removal efficiencies in ABR varied between 88-92% as NB concentrations increased from 30 to 210 mg/L. After this dose, COD removal efficiency decreased to 85 and 79% at NB concentrations of 550 and 700 mg/L, respectively. Removal efficiencies of NB were nearly 100% for all NB concentrations in ABR reactor effluent. In the second step, COD and NB concentrations were kept constant while HRT decreased from 10.38 days to 1 day. As HRT decreased from 10.38 to 2.5 days the COD removal efficiencies in the anaerobic and anaerobic/aerobic reactor effluents were 92-94% and 97-98%, respectively. As HRT decreased from 2.5 days to 1 day COD removal efficiencies in the anaerobic and anaerobic/aerobic reactor effluents decreased to 83 and 95%, respectively. This study showed that HRT is a more important operation parameter than increasing NB concentration in ABR/CSTR sequential reactor system. Although ABR/CSTR system exhibited good COD and NB removal efficiencies, the lower HRTs slightly decreased the removal efficiencies compared to increasing NB concentration.     

林可霉素高浓度有机废水处理技术

采用厌氧颗粒和好氧活性污泥分别对内循环厌氧反应器(IC)和间歇式活性污泥法(SBR)进行污泥接种培养,研究水解酸化-IC-SBR工艺在林可霉素生产废水处理方面的运行效果。结果表明:在进水COD的质量浓度为6 000~9 000 mg/L,IC和SBR反应器中有机负荷分别为0.82 kg/(kg.d)和0.26 kg/(kg.d)左右的情况下,IC和SBR反应器分别运行60 d和7 d,COD平均去除率分别达到91%和61%,出水COD的质量浓度在300 mg/L以下,达到GB 8978—1996《污水综合排放标准》二级标准。     

Anaerobic treatment of a medium strength industrial wastewater at low-temperature and short hydraulic retention time: a pilot-scale experience

The aim of this work was to evaluate the performance of a pilot-scale upflow anaerobic sludge blanket (UASB) reactor during the treatment of cereal-processing industry wastewater under low-temperature conditions (17 degrees C) for more than 300 days. The applied organic loading rate (OLR(appl)) was gradually increased from 4 to 6 and 8 kg COD(sol)/m3d by increasing the influent soluble chemical oxygen demand (COD(sol)), while keeping the hydraulic retention time constant (5.2 h). The removal efficiency was high (82 to 92%) and slightly decreased after increasing the influent COD(sol) and the OLR(appl). The highest removed organic loading rate (OLR(rem)) was reached when the UASB reactor was operated at 8 kg COD(sol)/m3d and it was two times higher than that obtained for an OLR(appl) of 4 kg COD(sol)/m3d. Some disturbances were observed during the experimentation. The formation of biogas pockets in the sludge bed significantly complicated the biogas production quantification, but did not affect the reactor performance. The volatile fatty acids in the effluent were low, but increased as the OLR(appl) increased, which caused an increment of the effluent COD(sol). Anaerobic treatment at low temperature was a good option for the biological pre-treatment of cereal processing industry wastewater.     

Denitrification of nitrate-contaminated groundwater using a simple immobilized activated sludge bioreactor

A simple anaerobic-activated sludge system, in which microorganisms are immobilized by a novel functional carrier, was used for removing nitrate in groundwater. The operating conditions, including hydraulic retention time (HRT), C/N ratio, temperature and NO(3)(-)-N loading concentration were investigated. The NO(3)(-)-N concentration, residual chemical oxygen demand (COD) and nitrite accumulation were used as indicators to assess the water quality of the effluent. The anaerobic biomass loading capacity in the carrier was 12.8 g/L and the denitrifying Pseudomonas sp. and Rhodocyclaceae bacterium were dominant among the immobilized microorganisms in the anaerobic-activated sludge. Under operating conditions of HRT= 1.5 h, C/N= 2-3 and T= 16.8-20 °C, the removal efficiency of NO(3)(-)-N exceeded 93%, corresponding to a relatively high denitrification rate of 0.73 kg NO(3)(-)-N m(-3) d(-1), when the NO(3)(-)-N loading concentration was 50 mg/L. The NO(3)(-)-N concentration of the effluent always met regulatory criteria for drinking water (<10 mg/L) in the main developed and developing countries. The effluent COD was also below 10 mg/L. Although some nitrite accumulated (0-1.77 mg/L) during the operating period, it can be decreased through adjusting the operating pH and HRT. The immobilized activated sludge system may be useful for the removal of nitrate from groundwater.     

深度处理维生素制药废水的中试研究

维生素制药废水经过初步生化处理后,出水水质无法满足要求,具有难降解、COD和氨氮浓度高的特点,针对这些特点,本文采用"强化复合曝气水解酸化→高效厌氧复合反应→流离生物接触氧化"连续工艺深度处理维生素制药废水,研究其可行性。处理规模为7.2 m3/d的中型试验结果表明:强化复合曝气水解酸化能使进水B/C值由0.33提高到0.48,提高下一步生化反应的处理效率,当进水CODCr的浓度为150～641 mg/L,氨氮浓度为6～115 mg/L时,平均去除率分别达到84.28%、93.8%,出水COD浓度小于50mg/L,氨氮浓度小于5 mg/L,出水水质能够达到《城镇污水处理厂污染物排放标准》GB18918-2002中的一级A指标,该连续工艺深度处理此类废水具有可行性和稳定性。     

Anaerobic digestion elutriated phased treatment of piggery waste.

The performance of a novel high-rate anaerobic process, the anaerobic digestion elutriated phased treatment (ADEPT) process, for treating a slurry-type piggery waste (55 g COD/L and 37 g TS/L) was investigated. The ADEPT process consists of an acid elutriation slurry reactor for hydrolysis and acidification, followed by an upflow anaerobic sludge bed reactor for methanification. This process provides stable and high system performance with short HRT (7.4 d) and better effluent quality (2 g SCOD/L and 0.68 g VSS/L) due to the alkaline pH condition for hydrolysis/acidification phase, high refractory solids removal and ammonia toxicity reduction. The optimum pH and HRT for hydrolysis/acidogenesis of the piggery waste were 9 and 5 days at both 35 degrees C and 55 degrees C conditions. The hydrolysis and acidification rate in the mesophilic reactor were 0.05 d(-1) and 0.11 d(-1), meaning that hydrolysis was a limiting step. SCOD production by the hydrolysis was about 0.26 g SCOD/g VS(fed) (3.6 g SCOD/g VS reduction). Methane production and content in the system were 0.3 L CH4/g VS(fed) (0.67 L CH4/g VS destroyed) and 80%, respectively, corresponding to 0.23 L CH4/g COD removal (@STP).     

Effects of ORP, recycling rate, and HRT on simultaneous sulfate reduction and sulfur production in expanded granular sludge bed (EGSB) reactors under micro-aerobic conditions for treating molasses distillery wastewater

An expanded granular sludge bed (EGSB) reactor was adopted to incubate the sludge biogranule that could simultaneously achieve sulfate reduction and sulfide reoxidization to elemental sulfur for treating molasses distillery wastewater. The EGSB reactor was operated for 175 days at 35 °C with a pH value of 7.0, chemical oxygen demand (COD) loading rate of 4.8 kg COD/(m3 d), and sulfate loading rate of 0.384 kg SO(4)(2-)/(m3 d). The optimal operation parameters, including the oxidation reduction potential (ORP), recycling rate, and hydraulic retention time (HRT), were established to obtain stable and acceptable removal efficiencies of COD, sulfate, and higher elemental sulfur production. With an ORP of -440 mV, a recycling rate of 300%, and HRT of 15 h, the COD and sulfate removal efficiencies were 73.4 and 61.3%, respectively. The elemental sulfur production ratio reached 30.1% when the elemental sulfur concentration in the effluent was 48.1 mg/L. The performance results were also confirmed by the mass balance calculation of sulfate, sulfide, and elemental sulfur over the EGSB reactor.     

Effects of solid retention time on the performance of submerged anoxic/oxic membrane bioreactor.

In this study, four similar bench-scale submerged Anoxic/Oxic Membrane Bioreactors (MBR) were used simultaneously to investigate the effects of solids retention time (SRT) on organic and nitrogen removal in MBR for treating domestic wastewater. COD removal efficiencies in all reactors were consistently above 94% under steady state conditions. Complete conversion of NH(4+)-N to NO(3-)-N was readily achieved over a feed NH(4+)-N concentration range of 30 to 50 mg/L. It was also observed that SRT did not significantly affect the nitrification in the MBR systems investigated. The average denitrification efficiencies for the 3, 5, 10 and 20 days SRT operations were 43.9, 32.6, 47.5 and 66.5%, respectively. In general, the average effluent nitrogen concentrations, which were mainly nitrate, were about 22.2, 27.6, 21.7 and 13.9 mg/L for the 3, 5, 10 and 20 days SRT systems, respectively. The rate of membrane fouling at 3 days SRT operation was more rapid than that observed at 5 days SRT. No fouling was noted in the 10 days and 20 days SRT systems during the entire period of study.     

Reliable method for assessing the COD mass balance of a submerged anaerobic membrane bioreactor (SAMBR) treating sulphate-rich municipal wastewater

The anaerobic treatment of sulphate-rich wastewater causes sulphate reducing bacteria (SRB) and methanogenic archaea (MA) to compete for the available substrate. The outcome is lower methane yield coefficient and, therefore, a reduction in the energy recovery potential of the anaerobic treatment. Moreover, in order to assess the overall chemical oxygen demand (COD) balance, it is necessary to determine how much dissolved CH(4) is lost in the effluent. The aim of this study is to develop a detailed and reliable method for assessing the COD mass balance and, thereby, to establish a more precise methane yield coefficient for anaerobic systems treating sulphate-rich wastewaters. A submerged anaerobic membrane bioreactor (SAMBR) treating sulphate-rich municipal wastewater was operated at 33 °C for an experimental period of 90 d, resulting in a high COD removal (approximately 84%) with a methane-enriched biogas of 54 ± 15% v/v. The novelty of the proposed methodology is to take into account the sulphide oxidation during COD determination, the COD removed only by MA and the dissolved CH(4) lost with the effluent. The obtained biomethanation yield (333 L CH(4) kg(-1) COD(REM MA)) is close to the theoretical value, which confirms the reliability of the proposed method.     

Integrated chemical, physical and biological processes modelling of anaerobic digestion of sewage sludge.

The biological kinetic processes for anaerobic digestion (AD) are integrated into a two phase subset of a three phase mixed weak acid/base chemistry kinetic model. The approach of characterising sewage sludge into carbohydrates, lipids and proteins, as is done in the International Water Association (IWA) AD model No 1 (ADM1), requires measurements that are not routinely available on sewage sludges. Instead, the sewage sludge is characterised with the COD, carbon, hydrogen, oxygen and nitrogen (CHON) composition and is formulated in mole units, based on conservation of C, N, O, H and COD. The model is calibrated and validated with data from laboratory mesophilic anaerobic digesters operating from 7 to 20 d sludge age and fed a sewage primary and humus sludge mixture. These digesters yielded COD mass balances between 107-109% and N mass balances between 91-99%, and hence the experimental data is accepted as reasonable. The sewage sludge COD is found to be 32-36% unbiodegradable (depending on the kinetic formulation selected for the hydrolysis process) and to have a C3.5H7O2N0.196 composition. For the selected hydrolysis kinetics of surface mediated reaction (Contois), with a single set of kinetic and stoichiometric constants, for all retention times good correlation is obtained between predicted and measured results for: (i) COD; (ii) free and saline ammonia (FSA); (iii) short chain fatty acids (SCFA); (iv) H2CO3 * alkalinity; (v) pH of the effluent stream; (vi) CO2; and (vii) CH4 gases in the gas stream. The measured composition of primary sludge from two local wastewater treatment plants ranged between C3.38H7O1.91 N0.21 and C3.91H7O2.04N0.16. The predicted composition based on mass balances is therefore within 5% of the average measured composition providing persuasive validation of the model.     

Anaerobic reactor/high rate pond combined technology for sewage treatment in the Mediterranean area.

Two high-rate, anaerobic/aerobic units were used to treat the sewage of the Institut Agronomique st Vétérinaire Hassan II (Morocco) campus in a 1,100 m2-plant designed for 1,500 e.p. and receiving 63 m3 per day. The anaerobic pre-treatment consisted of a two-step up-flow anaerobic reactor (TSUAR) comprising two reactors and one external settler all in series. The aerobic line, or post-treatment, consisted of a high-rate algal pond (HRAP) and one maturation pond in series. The system totalized a hydraulic retention time (HRT) of 9 days. A gravel filter (GF) was constructed behind the TSUAR to trap low-density particles. The TSUAR removed 80% of COD and 90% of SS within 48 h. Solids retention time in the reactors averaged 32 d with a specific sludge production of 0.28 g SS g(-1) COD removed. Almost 93% of the sludge evacuated from the settler was stabilized. Specific biogas production from both reactors was 0.25m3 kg(-1) COD removed. Used in this configuration, the HRAP lost its BOD removal activity and increased its nutrients and pathogens removal capabilities (tertiary treatment). Results showed that 85% of total nitrogen and 48% of total phosphorus were removed by the HRAP. Land area requirement of this combination was less than 1 m2 per capita and filtered final effluent was of excellent quality (COD, 82 mg/l; TKN, 8.3 mg/l; total P, 2.7 mg/l, faecal coliforms, 2.4 10(3)/100 ml and zero helminths eggs).     

Anaerobic co-digestion of winery wastewater.

The operational performance of anaerobic batch reactors treating winery wastewater (WW) combined with waste activated sludge (WAS) in different proportions was investigated under mesophilic conditions. In these experiments it was shown that for anaerobic digestion of WW alone, methane production rate was lower than the rates achieved when WW and WAS were treated together. When WW was mixed with WAS at a concentration of 50% WW resulted in the highest methane production rates. A simplified anaerobic model was used to determine the main kinetic parameters; maximum COD reduction rate (q(DA)) and maximum methane generation rate (k(max)). The maximum values of q(DA) and k(max) were 16.50 kgCOD COD(-1) d(-1) and 14.34 kgCOD kgCOD(-1) d(-1), respectively.     

Respirometric assays of two different MBR (microfiltration and ultrafiltration) to obtain kinetic and stoichiometric parameters

A comparison of two different medium scale MBRs (ultrafiltration and microfiltration) using respirometric methods has been achieved. The ultrafiltration membrane plant (0.034 microm pore size) maintained recirculation sludge flow at seven times the influent flow, and membranes were backwashed every 5 min and chemically cleaned weekly. The microfiltration membrane plant (0.4 microm pore size) maintained recirculation sludge flow at four times the influent flow, membrane-relax was applied after the production phase and membranes were chemically cleaned in the event of high trans-membrane pressure. Both technologies showed a similar performance with regard to heterotrophic kinetic and stoichiometric parameters and organic matter effluent concentrations. The influent was characterized by means of its COD fractions and the average removal percentages for COD concentrations were around 97% for both plants in spite of influent COD fluctuation, temperature variations and sludge retention time (SRT) evolution. Both SRT evolution and temperature affect the heterotrophic yield (Y(H)) and the decay coefficient (bH) in the same range for both plants. Y(H) values of over 0.8 mg COD/mg COD were obtained during the unsteady periods, while under steady state conditions these values fell to less than 0.4 mg COD/mg COD. bH by contrast reached values of less than 0.05 d(-1).     

Upgrading of Florence wastewater treatment plant: co-digestion and nitrogen autotrophic removal.

In recent years a completely autotrophic nitrogen removal process based on Anammox biomass has been tested in a few European countries in order to treat anaerobic supernatant and to increase the COD/N ratio in municipal wastewater. This work reports experimental results on a possible technical solution to upgrade the S. Colombano treatment plant which treats wastewater from the Florentine urban area. The idea is to use 50% of the volume of the anaerobic digester in order to treat external sewage sludge (as septic tank sludge) together with waste activated sludge and to treat the resulting effluent on a SHARON-ANAMMOX process in order to remove nitrogen from the anaerobic supernatant. Anaerobic co-digestion, tested in a 200 L pilot plant, enables low cost treatment of septic tank sludge and increases biogas production; however, it also increases the nitrogen load re-circulated to the WWTP, where nitrogen removal efficiency is already low (<50%), due to the low COD/N ratio, which limits predenitrification efficiency. Experimental results from a SHARON process tested in a lab-scale pilot plant show that nitrite oxidising bacteria are washed-out and steady nitrite production can be achieved at retention times in the range 1 - 1.5 days, at 35 degrees C. In a lab-scale SBR reactor, coupled with a nitration bioreactor, maximum specific nitrogen removal rate under nitrite-limiting conditions (with doubling time equal to about 26 days at 35 degrees C) was equal to 0.22 kgN/kgSSV/d, about 44 times the rate measured in inoculum Anammox sludge. Finally, a cost analysis of the proposed upgrade is reported.     

Use of the ADM1 to investigate the effects of acetoclastic methanogen population dynamics on mesophilic digester stability.

The ADM1 was employed to assess the effect of variations in solids hydrolysis and acetoclastic methanogen process characterizations on municipal digester stability relating to excess acetate utilization capacity. First-order single- and dual-pathway hydrolysis rate functions and single and competitive acetoclastic methanogen rate functions were implemented in the ADM1. The acetate capacity number (ACN), defined as the ratio between the maximum acetate utilization rate and the average acetate production rate, was used to index digester instability. Simulations of a single CSTR at steady state indicate a similar ACN can be obtained with a 12-day SRT digester dominated by Methanosarcina sp and a 24-day SRT digester dominated by Methanosaeta sp. An increase in ACN with a decrease in SRT representing Methanosarcina sp. selection was observed for particulate feed loadings from 40 g COD/L to 90 g COD/L. Feeding frequency and dual-pathway hydrolysis were found to have less effect on the ACN than the competitive acetoclastic model structure.     

Treatment of organic synthesis wastewater using anaerobic packed bed and aerobic suspended growth bioreactors.

The performance of an anaerobic mesophilic packed bed reactor, with a mixture of GAC and tezontle, followed by an aerobic suspended growth system was studied for the treatment of organic chemical wastewater with a high COD concentration (22-29 g/L). The testing of the anaerobic-aerobic system was conducted in an experimental set-up for almost 2.5 years. Different operational conditions were evaluated. The anaerobic reactor showed performance stability and COD removals higher than 80% were obtained with loads up to 16.6 kg x m(-3) x d(-1). The acclimation of the aerobic biomass to the substrate in the anaerobic effluent was very quick and COD removals higher than 94% were obtained even at high organic loads. The combined anaerobic-aerobic system allowed total COD removals higher than 99.5% and the accomplishment of the discharge requirements of 200 mgCOD/L when the anaerobic reactor was operated with loads of 8-11 kg x m(-3)x d(-1) and the aerobic reactor with 0.33 kg x kg(-1) x d(-1), being the total HRT of 4.4. The average TKN removal in the anaerobic-aerobic system was 97%, the average for the anaerobic reactor being 52% and that one for the aerobic system being 94%.     

Integrated biological (anaerobic-aerobic) and physico-chemical treatment of baker's yeast wastewater.

The UASB reactor (35 degrees C) was quite efficient for removal of bulk COD (52-74%) from simulated (on the basis of cultivation medium from the first separation process) general effluent of baker's yeast production (the average organic loading rates varied from 8.1 to 16 g COD/l/d). The aerobic-anoxic biofilter (19-23 degrees C) can be used for removal of remaining BOD and ammonia from anaerobic effluents; however, it suffered from COD-deficiency to fulfil denitrification requirements. To balance COD/N ratio, some bypass (approximately 10%) of anaerobically untreated general effluent should be added to the biofilter feed. The application of iron (III)-, aluminium- or calcium-induced coagulation for post-treatment of aerobic-anoxic effluents can fulfil the limits for discharge to sewerage (even for colour mainly exerted by hardly biodegradable melanoidins), however, the required amounts of coagulants were relatively high.     

Advanced treatment by anaerobic process followed by aerobic membrane bioreactor for effluent reuse in paper mill industry.

The operation of an activated sludge process at a paper mill (AIPM) in Hedera, Israel, was often characterized by disturbances. As part of a research and development project, a study on new biological treatment was initiated. The study included the operation of three pilot units: a. anaerobic treatment by upflow anaerobic sludge blanket (UASB); b. aerobic treatment by two pilot units including activated sludge and membrane bioreactor (MBR), which have been operated in parallel for comparison reasons. The pilot plant working on anaerobic treatment performed COD reduction from 2,365 to 755 mg/L, expressed as average values. Based on the pilot study, a full scale anaerobic treatment system has been erected. During a period of 100 days, after achieving steady state, the MBR system provided steady operation performance, while the activated sludge produced effluent characterized by oscillatory qualities. The following results, based on average values, indicate much lower suspended solids concentrations in the MBR effluent, 2.5 mg/L, as compared to 25 mg/L in the activated sludge. The ability to develop and maintain a concentration of over 11,000 mg/L of mixed liquor volatile suspended solids in the MBR enabled an intensive bioprocess at relatively high cell residence time. This study demonstrates that the anaerobic process, followed by aerobic MBR can provide effluent of high quality which can be considered for economic reuse in the paper mill industry.