Innovations in wastewater treatment: the moving bed biofilm process.

This paper describes the moving bed biofilm reactor (MBBR) and presents applications of wastewater treatment processes in which this reactor is used. The MBBR processes have been extensively used for BOD/COD-removal, as well as for nitrification and denitrification in municipal and industrial wastewater treatment. This paper focuses on the municipal applications. The most frequent process combinations are presented and discussed. Basic design data obtained through research, as well as data from practical operation of various plants, are presented. It is demonstrated that the MBBR may be used in an extremely compact high-rate process (<1 h total HRT) for secondary treatment. Most European plants require P-removal and performance data from plants combining MBBR and chemical precipitation is presented. Likewise, data from plants in Italy and Switzerland that are implementing nitrification in addition to secondary treatment are presented. The results from three Norwegian plants that are using the so-called combined denitrification MBBR process are discussed. Nitrification rates as high as 1.2 g NH4-N/m2 d at complete nitrification were demonstrated in practical operation at low temperatures (11 degrees C), while denitrification rates were as high as 3.5g NO3-Nequiv./m2.d. Depending on the extent of pretreatment, the total HRT of the MBBR for N-removal will be in the range of 3 to 5 h.     

Effect of organic load and nutrient ratio on the operation stability of the moving bed bioreactor for kraft mill wastewater treatment and the incidence of polyhydroxyalkanoate biosynthesis

This paper studies the effect of organic load rate (OLR) and nutrient ratio on operation stability of the moving bed bioreactor (MBBR) for kraft mill wastewater treatment, analyzing the incidence of polyhydroxyalkanoate (PHA) production. The MBBR operating strategy was to increase OLR from 0.25 ± 0.05 to 2.41 ± 0.19 kg COD m(-3) d(-1) between phases I and IV. The BOD(5):N:P ratio (100:5:1 and 100:1:0.2) was evaluated as an operation strategy for phases IV to V. A stable MBBR operation was found when the OLR was increased during 225 days in five phases. The maximum absolute fluorescence against the proportion of cells accumulating PHA was obtained for an OLR of 2.41 ± 0.19 kg COD m(-3)d(-1) and a BOD(5):N:P relationship of 100:1:0.2. The increase of PHA biosynthesis is due to the increased OLR and is not attributable to the increased cell concentration, which is maintained constant in stationary status during bioreactor biosynthesis.     

Comparison between a moving bed bioreactor and a fixed bed bioreactor for biological phosphate removal and denitrification

Moving bed bioreactors (MBBR) and fixed bed bioreactors (FBBR) were compared for biological phosphorus removal and denitrification. The sorption denitrification P-elimination (S-DN-P) process was selected for this study. Results indicated that all nutrients were removed by the FBBR process compared with the MBBR process: 19.8% (total COD), 35.5% (filtered COD), 27.6% (BOD(5)), 62.2% (acetate), 78.5% (PO(4)-P), and 54.2% (NO(3)-N) in MBBR; 49.7% (total COD), 54.0% (filtered COD), 63.2% (BOD(5)), 99.6% (acetate), 98.6% (PO(4)-P), and 75.9% (NO(3)-N) in FBBR. The phosphate uptake and NO(3)-N decomposition in the FBBR process during the denitrification phase were much higher than for the MBBR process despite being of shorter duration. Results obtained from this study are helpful in elucidating the practical implications of using MBBR and FBBR for the removal of bio-P and denitrification from wastewater.     

Application of a combined process of moving-bed biofilm reactor (MBBR) and chemical coagulation for dyeing wastewater treatment.

A combined process consisted of a Moving-Bed Biofilm Reactor (MBBR) and chemical coagulation was investigated for textile wastewater treatment. The pilot scale MBBR system is composed of three MBBRs (anaerobic, aerobic-1 and aerobic-2 in series), each reactor was filled with 20% (v/v) of polyurethane-activated carbon (PU-AC) carrier for biological treatment followed by chemical coagulation with FeCl2. ln the MBBR process, 85% of COD and 70% of color (influent COD = 807.5 mg/L and color = 3,400 PtCo unit) were removed using relatively low MLSS concentration and short hydraulic retention time (HRT = 44 hr). The biologically treated dyeing wastewater was subjected to chemical coagulation. After coagulation with FeCl2, 95% of COD and 97% of color were removed overall. The combined process of MBBR and chemical coagulation has promising potential for dyeing wastewater treatment.     

改进型移动床生物膜反应器处理有机废水的试验

改进型移动床生物膜反应器(CMCBR)是在普通移动床生物膜反应器中引入导流板,使填料在全池循环移动,消除了普通移动床生物膜反应器的死角。在CMCBR处理模拟生活污水的试验中,研究了有机物的去除效果,考察了容积负荷、水力停留时间、冲击负荷等参数对处理效果的影响。试验发现,在填料填充比例为50%(体积比),进水COD质量浓度为320~550mg/L,水力停留时间为3 h的条件下,出水COD质量浓度小于100 mg/L,达到国家污水综合排放标准的一级标准。反应器具有较强的抗冲击负荷能力,出水水质稳定。     

The impact of cleaner processing on nutrient availability in the bleached kraft industry.

The pulp and paper industry has invested heavily over recent years in cleaner processing, to reduce losses and minimise its impact on the environment. Over the past fifteen years, a New Zealand integrated bleached kraft mill has undergone a comprehensive programme of upgrades to increase production, reduce water consumption and streamline its biological treatment process. Whilst the overall discharge of contaminants from the site decreased, the treatment system performance did not show a concurrent improvement as may have been expected. Reduced BOD removal, low dissolved oxygen levels, and poor solids settlability were symptomatic of phosphorus limitation in the aerated lagoon treatment system. The wastewater entering the system was found to be phosphorus limited at a BOD:P ratio of 100:0.2. Mono-ammonium-phosphate was supplemented, at approximately 30 kg P/d, to raise the phosphorus levels to a BOD:P ratio of 100:0.3. Treatment efficiencies improved very quickly after phosphorus dosage, with a 50% reduction in BOD and TSS discharge, a significant increase in dissolved oxygen levels, and improved BOD removal (85% to 93%). This case study demonstrates that whilst more closed operation can result in reduced discharge of organic loads, there may be negative impacts on the availability of nutrients for balanced biological growth.     

Kinetic study of slaughterhouse wastewater treatment by electrocoagulation using Fe electrodes

In this study, treatment of slaughterhouse wastewater by electrocoagulation was investigated in batch system using Fe electrodes. The effect of various variables such as electrode number, current density and operating time was tested. Pollutant removal efficiency increased with increasing electrode number and operating time. The biochemical oxygen demand (BOD(5))(,) chemical oxygen demand (COD), total suspended solid (TSS), and total nitrogen (TN) removal efficiencies using eight electrodes at a contact time of 50 min and a current density of 10 A/m(2) were 66, 62, 60, and 56%, respectively. Higher electrode numbers will allow shorter operating times to achieve certain removal efficiencies. Also, removal efficiencies increased by increasing the current density; the highest removal efficiencies of BOD(5,) COD, TSS, and TN at a contact time of 50 min and a current density of 25 A/m(2) were 97, 93, 81, and 84%, respectively. The results also show that the reactor pH varies directly with the current density; at 25 A/m(2), the reactor pH increased from an initial value of 7.1 to 7.7 after 50 min. The experimental results showed that the kinetics of BOD(5), COD, TSS and TN removal could be fitted adequately using a first order kinetic model (higher R(2)).     

Leachate detoxification by combination of biological and TiO2-photocatalytic processes.

Landfill leachates are a problematic wastewater due to their variable concentration, volume changing in time and presence of refractory and hazardous components. In this paper, the results of a new approach to photocatalysis assisted by biological process for the detoxification of stabilised landfill leachate are presented. The biologically pre-treated leachate still contained a significant amount of non-biodegradable COD and TOC amounting to 500 and 200 mg/L, respectively. The 300 min of photocatalytic treatment (UVC/TiO2) brought about a significant decrease in more than 80% refractory organics remaining in leachate. The effect of pH and catalyst loading on mineralisation, colour removal rate and biodegradability (BOD/COD) improvement in the photoreactor were discussed. The bio-accessibility of formed photocatalytic oxidation intermediates was confirmed by oxygen uptake rate (OUR) measurements. Consequently, a part of COD was successfully removed in post-biological treatment.     

A calibration protocol of a one-dimensional moving bed bioreactor (MBBR) dynamic model for nitrogen removal

This work suggests a procedure to correctly calibrate the parameters of a one-dimensional MBBR dynamic model in nitrification treatment. The study deals with the MBBR configuration with two reactors in series, one for carbon treatment and the other for nitrogen treatment. Because of the influence of the first reactor on the second one, the approach needs a specific calibration strategy. Firstly, a comparison between measured values and simulated ones obtained with default parameters has been carried out. Simulated values of filtered COD, NH(4)-N and dissolved oxygen are underestimated and nitrates are overestimated compared with observed data. Thus, nitrifying rate and oxygen transfer into the biofilm are overvalued. Secondly, a sensitivity analysis was carried out for parameters and for COD fractionation. It revealed three classes of sensitive parameters: physical, diffusional and kinetic. Then a calibration protocol of the MBBR dynamic model was proposed. It was successfully tested on data recorded at a pilot-scale plant and a calibrated set of values was obtained for four parameters: the maximum biofilm thickness, the detachment rate, the maximum autotrophic growth rate and the oxygen transfer rate.     

Multi-component kinetics of activated sludge treatment of bleached kraft mill effluent.

This study investigated the discrepancies between the BOD removal rates measured during short term assays and those measured during continuous activated sludge treatment of bleached kraft mill effluent (BKME). A combination of batch tests and fed batch tests with oxygen uptake rate (OUR), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and mixed liquor volatile suspended solids (MLVSS) measurements were used to characterize the degradation rates for the activated sludge treatment of BKME and to divide the soluble readily biodegradable substrate into two to five separate fractions based on biodegradation rates. The removal rates varied by over an order of magnitude between the most readily degradable substrates (1 x 10(-3) mg COD/mg MLVSS minute), and the more slowly degradable substrates (2 x 10(-5) mg COD/mg MLVSS minute). If the readily biodegradable fraction of BKME was modeled as one substrate, initial rate kinetic measurements from batch tests were heavily influenced by the fractions with the greatest degradation rates, while any remaining BOD in the treated effluent was predominantly from the slowly degradable fraction, giving inconsistent results. Taking the multi-component nature of the wastewater into account, batch test results can be used to predict fed-batch and continuous activated sludge reactor performance.     

SBR工艺动力学研究与工程应用

棉浆粕废水组分较为复杂,治理具有一定的技术难度,采用两相厌氧、序批式活性污泥法和物化处理组合工艺取得了较好的效果。生产运行结果表明:SBR工艺对COD,BOD的去除效率分别达到40％～57％和55％～70％。在水温自然变化情况下,测定了好氧SBR单元的生化动力学参数,并与已有文献报道的纸浆和造纸废水的测定结果进行了比较,表明棉浆粕废水经两相厌氧处理后的出水更易于生化处理,但仍属较难好氧生化处理废水。     

Long-term evaluation of a sequential batch reactor (SBR) treating dairy wastewater for carbon removal.

Many dairy industries have been using SBR wastewater treatment plants because they allow optimal working condition to be reached. However, to take advantage of SBR capabilities, strong process automation is needed. The aim of this work is to study the factors that influence SBR performance to improve modelling and control. To better understand the whole process we studied the kinetic modelling, the carbon removal mechanism and the relation between reactor performance, aerobic heterotrophic activity and bacterial population dynamics (by terminal restriction fragment length polymorphisms of 16S rDNA, T-RFLP). The heterotrophic activity values presented high variability during some periods; however, this was not reflected on the reactor performance. As sludge health indicator, the average activity in a period was better than individual values. Although all the carbon removal mechanisms are still unclear for this process, they seemed to be influenced by non-respirometric ways (storage, biosorption, accumulation, etc.). The variability of heterotrophic activity could be correlated with the bacterial population diversity over time. Despite the high variability of the activity, a simple kinetic model (pseudo ASM1) based on apparent constant parameters was developed and calibrated. Such modellisation provided a good tool for control purposes.     

Oxidative processes for olive mill wastewater treatment.

The present work describes an experimental study carried out in order to investigate the efficiency and feasibility of physical (lime coagulation) and advanced oxidation processes (Ozone and Fenton's process) for olive oil mill wastewater treatment. Particular attention was paid to the degradation of both organic and phenolic compounds. Lime coagulation reaches maximum removal at a pH of 12, with a TP (total polyphenols) and COD reduction of 37 and 26%, respectively. Ozone oxidation is also pH-dependent, showing the higher removal efficiency (91% for TP and 19% for COD) with an initial pH value of 12. Experimental results show a lower efficiency of Fenton's process than ozone in TP removal, reaching a maximum value of 60%. Oxidation trials carried out on gallic and p-coumaric synthetic solutions confirmed ozone and Fenton's efficiency at degrading phenolic compounds. Biological trials, both aerobic and anaerobic, highlighted a significant increase of biodegradability of treated OMW samples if compared to the untreated ones. Respirometric tests showed an increase in BOD of about 20% and anaerobic batch tests provided a methane production up to eight times higher.     

Effect of organic loading rate on a wastewater treatment process combining moving bed biofilm and membrane reactors.

The effect of moving bed biofilm reactor (MBBR) loading rate on membrane fouling rate was studied in two parallel units combining MBBR and membrane reactor. Hollow fiber membranes with molecular weight cut-off of 30 kD were used. The HRTs of the MBBRs varied from 45 min to 4 h and the COD loading rates ranged from 4.1 to 26.6 g COD m(-2) d(-1). The trans-membrane pressure (TMP) was very sensitive to fluxes for the used membranes and the experiments were carried out at relatively low fluxes (3.3-5.6 l m(-2) h(-1)). Beside the test with the highest flux, there were no consistent differences in fouling rate between the low- and high-rate reactors. Also, the removal efficiencies were quite similar in both systems. The average COD removal efficiencies in the total process were 87% at 3-4 h HRT and 83% at 0.75-1 h HRT. At high loading rates, there was a shift in particle size distribution towards smaller particles in the MBBR effluents. However, 79-81% of the COD was in particles that were separated by membranes, explaining the relatively small differences in the removal efficiencies at different loading rates. The COD fractionation also indicated that the choice of membrane pore size within the range of 30 kD to 0.1 microm has very small effect on the COD removal in the MBBR/membrane process, especially with low-rate MBBRs.     

Single-objective vs. multi-objective autocalibration in modelling total suspended solids and phosphorus in a small agricultural watershed with SWAT

To obtain greater precision in modelling small agricultural watersheds, a shorter simulation time step is beneficial. A daily time step better represents the dynamics of pollutants in the river and provides more realistic simulation results. However, with a daily evaluation performance, good fits are rarely obtained. With the Shuffled Complex Evolution (SCE) method embedded in the Soil and Water Assessment Tool (SWAT), two calibration approaches are available, single-objective or multi-objective optimization. The goal of the present study is to evaluate which approach can improve the daily performance with SWAT, in modelling flow (Q), total suspended solids (TSS) and total phosphorus (TP). The influence of weights assigned to the different variables included in the objective function has also been tested. The results showed that: (i) the model performance depends not only on the choice of calibration approach, but essentially on the influential parameters; (ii) the multi-objective calibration estimating at once all parameters related to all measured variables is the best approach to model Q, TSS and TP; (iii) changing weights does not improve model performance; and (iv) with a single-objective optimization, an excellent water quality modelling performance may hide a loss of performance of predicting flows and unbalanced internal model components.     

The impact of reduced phosphorus levels on microbial floc properties during biological treatment of pulp and paper wastewaters.

The effect of limiting P in activated sludge was investigated in laboratory scale sequencing batch reactors (SBRs) fed effluent from a container board mill. Floc characterization included measurement of hydrophobicity, surface charge, and analysis of extracellular polymeric substances (EPS). Reactor performance was assessed by monitoring COD and inorganic P removal, MLSS, and sludge settleability (SVI and batch settling flux) over a period of eight months. Control reactors (BOD:N:P of 100:5:1) were compared to reactors run under P-limited conditions (100:5:0.3; 100:5:0.1). Reactor performance at lower temperatures (14 degrees C; control = 26 degrees C) was also studied to assess the impact of P-limitation. Changes in floc structure and the composition of EPS occurred within 1 to 3 days following a reduction in P levels. There was an insignificant increase in SVI; however, gravitational settling velocity and batch settling flux values for low P floc were consistently higher than for floc generated under control conditions. Lower temperatures (14 degrees C) resulted in a deterioration in floc settling properties at a BOD:N:P of 100:5:1. This impact on settling was significantly reduced at a BOD:P of 100:0.1. Reducing P concentrations in the wastewater treatment system has the potential to improve sludge settleability and reduce final P discharges.     

Treatment of wastewater from a cotton dyeing process with UV/H2O2 using a photoreactor covered with reflective material

Wastewater containing several dyes, including sulfur black from the dyeing process in a textile mill, was treated using a UV/H2O2 process. The wastewater was characterized by a low BOD/COD ratio, intense color and high acute toxicity to the algae species Pseudokirchneriella subcaptata. The influence of the pH and H2O2 concentration on the treatment process was evaluated by a full factorial design 22 with three replicates of the central experiment. The removal of aromatic compounds and color was improved by an increase in the H2O2 concentration and a decrease in pH. The best results were obtained at pH 5.0 and 6 g L(-1). With these conditions and 120 min of UV irradiation, the removal of the color, aromatic compounds and COD were 74.1, 55.1 and 44.8%, respectively. Under the same conditions, but using a photoreactor covered with aluminum foil, the removal of the color, aromatic compounds and COD were 92.0, 77.6 and 59.4%, respectively. Moreover, the use of aluminum foil reduced the cost of the treatment by 40.8%. These results suggest the potential application of reflective materials as a photoreactor accessory to reduce electric energy consumption during the UV/H2O2 process.     

Evaluation of sludge properties in a pilot-scale UASB reactor for sewage treatment in a temperate region

In this study, continuous operation of a pilot-scale upflow anaerobic sludge blanket (UASB) reactor for sewage treatment was conducted for 630 days to investigate the physical and microbial characteristics of the retained sludge. The UASB reactor with a working volume of 20.2 m(3) was operated at ambient temperature (16-29 °C) and seeded with digested sludge. After 180 days of operation, when the sewage temperature had dropped to 20 °C or lower, the removal efficiency of both total suspended solids (TSS) and total biochemical oxygen demand (BOD) deteriorated due to washout of retained sludge. At low temperature, the cellulose concentration of the UASB sludge increased owing to the rate limitation of the hydrolytic reaction of suspended solids in the sewage. However, after an improvement in sludge retention (settleability and concentration) in the UASB reactor, the process performance stabilized and gave sufficient results (68% of TSS removal, 75% of total BOD removal) at an hydraulic retention time (HRT) of 9.7 h. The methanogenic activity of the retained sludge significantly increased after day 246 due to the accumulation of Methanosaeta and Methanobacterium following the improvement in sludge retention in the UASB reactor. Acid-forming bacteria from phylum Bacteroidetes were detected at high frequency; thus, these bacteria may have an important role in suspended solids degradation.     

A low-cost municipal sewage treatment system with a combination of UASB and the "fourth-generation" downflow hanging sponge reactors.

This paper presents an evaluation of the process performance of a pilot-scale "fourth generation" downflow hanging sponge (DHS) post-treatment system combined with a UASB pretreatment unit treating municipal wastewater. After the successful operation of the second- and third-generation DHS reactors, the fourth-generation DHS reactor was developed to overcome a few shortcomings of its predecessors. This reactor was designed to further enhance the treatment efficiency and simplify the construction process in real scale, especially for the application in developing countries. Configuration of the reactor was modified to enhance the dissolution of air into the wastewater and to avert the possible clogging of the reactor especially during sudden washout from the UASB reactor. The whole system was operated at a total hydraulic retention time (HRT) of 8 h (UASB: 6 h and DHS: 2 h) for a period of over 600 days. The combined system was able to remove 96% of unfiltered BOD with only 9 mg/L remaining in the final effluent. Likewise, F. coli were removed by 3.45 log with the final count of 10(3) to 10(4) MPN/100 ml. Nutrient removal by the system was also satisfactory.     

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.