Combined anaerobic digestion and biological nitrogen removal for piggery wastewater treatment: a modelling approach

In order to deal with the environmental problems associated with animal production industrialization and at the same time considering energy costs increasing, a piggery wastewater treatment process consisting of combined anaerobic digestion and biological nitrogen removal by activated sludge was developed. This contribution presents a modelling framework in order to optimize this process. Modified versions of the well established ASM1 and ADM1 models have been used. The ADM1 was extended with biological denitrification. pH calculation and liquid gas-transfer were modified to take into account the effect of associated components. Finally, two interfaces (ADMtoASM and ASMtoADM) were built in order to combine both models. These interfaces set up the COD, nitrogen, alkalinity and charge fractionation between both models. However, for the mass balances between both models, some hypotheses were considered and might be evaluated.     

Winery and distillery wastewater treatment by anaerobic digestion.

Anaerobic digestion is widely used for wastewater treatment, especially in the food industries. Generally after the anaerobic treatment there is an aerobic post-treatment in order to return the treated water to nature. Several technologies are applied for winery wastewater treatment. They are using free cells or flocs (anaerobic contact digesters, anaerobic sequencing batch reactors and anaerobic lagoons), anaerobic granules (Upflow Anaerobic Sludge Blanket--UASB), or biofilms on fixed support (anaerobic filter) or on mobile support as with the fluidised bed. Some technologies include two strategies, e.g. a sludge bed with anaerobic filter as in the hybrid digester. With winery wastewaters (as for vinasses from distilleries) the removal yield for anaerobic digestion is very high, up to 90-95% COD removal. The organic loads are between 5 and 15 kgCOD/m3 of digester/day. The biogas production is between 400 and 600 L per kg COD removed with 60 to 70% methane content. For anaerobic and aerobic post-treatment of vinasses in the Cognac region, REVICO company has 99.7% COD removal and the cost is 0.52 Euro/m3 of vinasses.     

Nitrogen removal from piggery waste with anaerobic pretreatment.

Aerobic degradation of high strength piggery waste elevated the reactor temperature inhibiting nitrification. This study included anaerobic pretreatment with various influent by-pass rates to control the temperature and to minimize the external carbon requirement for denitrification. To find the optimum operating conditions, both lab-scale AnSBR (anaerobic sequencing batch reactor) and Ax/Ox (anoxic/oxic) SBR were operated at 35 degrees C. The heat energy released from Ax/Ox SBR was assumed to be used for heating the AnSBR, with which the Ax/Ox reactor temperature could successfully be controlled below 40 degrees C. The optimum rates of by-pass were 1.0 for winter, 0.4 for spring/fall and 0.2-0.4 for summer, respectively. Applying the correction factors for the measured AUR2 (nitrite nitrification rate) and AUR (nitrate nitrification) at the predicted temperatures, the required oxic HRTs were computed. The required Ax/Ox HRT ratios were respectively 0.5 for COD/TKN>8, 1.0 for COD/TKN ratio of 5.5-8 and 3.5 for below 5.5. The optimum HRTs were 16 days for AnSBR and 17 days for Ax/Ox SBR with the corrected AUR2.     

Full-cyclic control strategy of SBR for nitrogen removal in strong wastewater using common sensors.

A full-cyclic automatic control strategy for sequencing batch reactors (SBR) was proposed using only common sensors such as ORP, DO and pH. The main objective was to develop a generally applicable and robust control strategy. To accomplish this, various control schemes found in the literature or suggested by authors were examined at diverse ammonia loads and SCOD/NH4(+)-N ratios. Advantages and constraints of each scheme were discussed and compared. Ammonia load was estimated with DO lag time during the aerobic stage, and then the influent pump was manipulated to meet the desired load at the next anoxic stage. A partial denitrification scheme was chosen for the anoxic stage period control, to save anoxic time and external carbon. For external carbon dosage control, intermittent feeding at each anoxic stage was concluded to be a suitable scheme. The anoxic stage period could be successfully controlled by the combination of pH increase and DO increase. Every suggested control scheme was incorporated into a full-cyclic control strategy and tested at 0.02, 0.035, 0.08 kg NH4(+)-N/m3/sub-cycle. From the results, it is expected to perform unmanned automatic SBR operation with this strategy.     

Enhanced nitrogen removal using C/N load adjustment and real-time control strategy in sequencing batch reactors for swine wastewater treatment.

The laboratory-scale sequencing batch reactor (SBR) was used to study the effectiveness of an integrated strategy of real time control with C/N ratio adjustment for practical swine wastewater treatment. Swine waste was used as the external carbon source for continuous treatment in the SBR reactors. Oxidation-reduction potential and pH were used as parameters to control the continuous denitrification and nitrification process, respectively. A constant effluent quality could be obtained, despite drastic variations in the characteristics of influent wastewater. Also, a relatively complete removal of nutrients was always ensured, since the optimum quantity of the external carbon source could be provided for complete denitrification, and a flexible hydraulic retention time was achieved by the successful real-time control strategy. The average removal efficiencies of total organic carbon and nitrogen were over 94% and 95%, respectively.     

Treatment of wine distillery wastewater by high rate anaerobic digestion.

Wine distillery wastewaters (WDW) are acidic and have a high content of potential organic pollutants. This causes high chemical oxygen demand (COD) values. Polyphenols constitute a significant portion of this COD, and limit the efficiency of biological treatment of WDWs. WDW starting parameters were as follows: pH 3.83, 4,185 mg/l soluble COD (COD(s)) and 674.6 mg/l of phenols. During operation, amendments of CaCO3 and K2HPO4, individually or in combination, were required for buffering the digester. Volatile fatty acid concentrations were < 300 mg/l throughout the study, indicating degradation of organic acids present. Mean COD(s) removal efficiency for the 130 day study was 87%, while the mean polyphenol, removal efficiency was 63%. Addition of 50 mg/l Fe(3+) between days 86 and 92 increased the removal efficiencies of COD(s) to 97% and of polyphenols to 65%. Addition of Co(3+) improved removal efficiencies to 97% for COD(s) and 92% for polyphenols. Optimization of anaerobic treatment was achieved at 30% WDW feed strength. Removal efficiencies of 92% and 84% were recorded at increased feed strength from days 108 to 130. High removal efficiencies of COD(s) and polyphenols after day 82 were attributed to the addition of macronutrients and micronutrients that caused pH stability and thus stimulated microbial activity.     

Resource recovery and nitrogen removal from piggery waste using the combined anaerobic processes.

The combined ADEPT (Anaerobic Digestion Elutriated Phased Treatment)- SHARON (Single reactor system High Ammonium Removal Over Nitrite)--ANAMMOX (Anaerobic Ammonium Oxidation) processes were operated for the purpose of resource recovery and nitrogen removal from slurry-type piggery waste. The ADEPT operated at acidogenic loading rates of 3.95 gSCOD/L-day, the SCOD elutriation rate and acid production rate were 5.3 gSCOD/L-day and 3.3 gVFAs(as COD)/L-day, respectively. VS reduction and SCOD reduction by hydrolysis were 13% and 0.19 gSCOD(prod.)/gVS(feeding), respectively. Also, the acid production rate was 0.80 gVFAs/gSCOD(production). In the methanogenic reactor, the gas production rate and methane content were 2.8 L/day (0.3 m3CH4/kgCOD(removal)STP) and 77%, respectively. With these operating condition, the removal of nitrogen and phosphorus were 94.1% as NH4-N (86.5% as TKN) and 87.3% as T-P, respectively.     

Nitrogen and phosphorus removal from swine wastewater by intermittently aerated dynamic-flow system.

This study was performed to evaluate the effects of the volume fraction of an anaerobic reactor (VFAR) and SRT on the removal of T-N and T-P in both an intermittently aerated system (IAS) and intermittently aerated dynamic-flow system (IADS), respectively. When the VFAR in the total volume of reactor from both IAS and IADS are 13%, 7%, and 0% at 5 days of SRT, the removal efficiencies of T-P were 80-87%, 62-65% and <30%, respectively. However, it was observed from this study that the removal efficiencies of T-N and T-P were not correlated to VFAR at a predetermined SRT, producing greater than 5000 mg/L of MLVSS. Also, IADS was shown to have the greater buffer capacity and adaptability to resist the shock due to the loading of high concentration of N. Furthermore, IADS achieved over 80% of removal efficiency of N even at much lower C/N ratio of 4.7. Therefore, it seems that IADS has the significant advantages over other biological nutrients removal processes.     

Phosphorus recovery from anaerobic digester supernatant by struvite crystallization: model-based evaluation of a fluidized bed reactor

This paper is an attempt to model the UBC (University of British Columbia) MAP (Magnesium Ammonium Phosphate) fluidized bed crystallizer. A mathematical model is developed based on the assumption of perfect size classification of struvitre crystals in the reactor and considering the movement of liquid phase as a plug flow pattern. The model predicts variation of species concentration of struvite along the crystal bed height. The species concentrations at two extreme ends (inlet and outlet) are then used to evaluate the reactor performance. The model predictions provide a reasonable good fit with the experimental results for both PO4-P and NH4-N removals. Another important aspect of this model is its capability of predicting the crystals size and the bed voidage at different height of the reactor. Those predictions also match fairly well with the experimental observations. Therefore, this model can be used as a tool for performance evaluation of the reactor and can also be extended to optimize the struvite crystallization process in the UBC MAP reactor.     

New anaerobic process of nitrogen removal.

This paper reports on successful laboratory testing of a new nitrogen removal process called DEAMOX (DEnitrifying AMmonium OXidation) for the treatment of strong nitrogenous wastewater such as baker's yeast effluent. The concept of this process combines the recently discovered ANAMMOX (ANaerobic AMMonium OXidation) reaction with autotrophic denitrifying conditions using sulfide as an electron donor for the production of nitrite within an anaerobic biofilm. The achieved results with a nitrogen loading rate of higher than 1,000 mg/L/d and nitrogen removal of around 90% look very promising because they exceed (by 9-18 times) the corresponding nitrogen removal rates of conventional activated sludge systems. The paper describes also some characteristics of DEAMOX sludge, as well as the preliminary results of its microbiological characterization.     

Performance evaluation of SBR treatment for nitrogen removal from tannery wastewater.

Performance of SBR treatment for nitrogen removal from tannery is evaluated for a wide range of wastewater temperature between 7 and 30 degrees C. A pilot-scale SBR unit fed with plain-settled wastewater is operated on site for this purpose. Effective nitrogen removal is sustained by adjustment of the sludge age from 28 to 5 days. Concentration profiles of nitrogen compounds within a selected complete SBR cycle during the steady state operation at different wastewater temperatures and sludge ages are evaluated by model simulation. System performance is also interpreted in terms of modeling and stoichiometric calculation. Additional nitrate loss was observed during aerobic period when the aeration intensity was reduced by the factor of 50%.     

Autotrophic nitrogen removal from anaerobic supernatant of Florence's WWTP digesters.

In municipal WWTP with anaerobic sludge digestion, 10-20% of total nitrogen load comes from the return supernatant produced by the final sludge dewatering. 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 the experimental results of the SHARON-ANAMMOX process application to anaerobic supernatant taken from the urban Florentine area wastewater treatment plant (S. Colombano WWTP). A nitritation labscale chemostat (7.4 L) has been started-up seeded with the S. Colombano WWTP nitrifying activated sludge. During the experimental period, nitrite oxidising bacteria wash-out was steadily achieved with a retention time ranging from 1 to 1.5 d at 35 degrees C. The Anammox inoculum sludge was taken from a pilot plant at EAWAG (Zurich). Anammox biomass has been enriched at 33 degrees C with anaerobic supernatant diluted with sodium nitrite solution until reaching a maximum specific nitrogen removal rate of 0.065 kgN kg(-1) VSS d(-1), which was 11 times higher than the one found in inoculum sludge (0.005 kgN kg(-1) VSS d(-1). In a lab-scale SBR reactor (4 L), coupled with nitritation bioreactor, specific nitrogen removal rate (doubling time equal to 26 d at 35 degrees C and at nitrite-limiting condition) reached the value of 0.22 kgN kg(-1) VSS d(-1), which was approximately 44 times larger than the rate measured in the inoculum Anammox sludge.     

Development of a new type of anaerobic digestion process equipped with the function of nitrogen removal.

In order to develop a new type of anaerobic digestion process equipped with a nitrogen removal function, denitrification of nitrate nitrogen (NO3-N) in anaerobic acidogenesis of organic fraction of municipal waste (OFMSW) was investigated by two semi-continuous reactors. Reactor 1 and Reactor 2 were fed by 3% and 7% of solids concentration of synthetic garbage, respectively. Generation of nitrogen gas (N2) and ammonium nitrogen (NH4-N) was simultaneously observed in the low load of nitrate (NO3-N) (below 0.68 g NO3-N/L). In Reactor 1, ammonium nitrogen generation decreased as the addition of nitrate increased. Finally, the increase of the addition of nitrate resulted in the increase of acetic acid production.     

磷酸铵镁和磷酸钙法处理厌氧上清液的比较

比较了Mg:P和Ca:P物质的量之比、pH及碳酸盐碱度对磷酸铵镁(MAP)和羟基磷灰石(HAP)结晶法去除厌氧出水中磷的影响,并对产物进行了扫描电镜-能谱分析(SEM-EDX).结果表明,在磷酸盐浓度为63 mg/L、pH为7.4的条件下,MAP法的除磷率最高能达47.9%,HAP法除磷率最高达40%.当pH升高到8.5～9.0,MAP法除磷率可达95%,出水pH小于8.0;为达到相同去除率,HAP法的pH需升高到9.5～10.0,其出水的pH为8.0～8.5.MAP法除磷更易得到较高纯度的晶体产物,且CO2-3对MAP晶体的纯度无明显影响,而HAP法除磷所得的产物中含有非晶态杂质.     

Control of C/N ratio for butyric acid production from textile wastewater sludge by anaerobic digestion

Increasing textile wastewaters and their biotreatment byproduct-waste activated sludge are serious pollution problems. Butyric acid production from textile wastewater sludge by anaerobic digestion at different C/N ratios was investigated. Adding starch to textile wastewater sludge with a C/N ratio of 30 increased the butyric acid concentration and percentage accounting for total volatile fatty acids (TVFAs) to 21.42 g/L and 81.5%, respectively, as compared with 21.42 g/L and 10.6% of textile wastewater sludge alone. The maximum butyric acid yield (0.45 g/g VS), conversion rate (0.74 g/g VS(digest)) and production rate (2.25 g/L d) was achieved at a C/N ratio of 30. The biological toxicity of textile wastewater sludge also significantly decreased after the anaerobic digestion. The study indicated that the anaerobic co-digestion of textile wastewater sludge and carbohydrate-rich waste with appropriate C/N ratio is possible for butyric acid production.     

ANAMMOX and partial denitritation in anaerobic nitrogen removal from piggery waste.

The anaerobic ammonium removal from a piggery waste with high strength (56 g COD/L and 5 g T-N/L) was investigated using a lab-scale upflow anaerobic sludge bed reactor at a mesophilic condition. Based on the nitrogen and carbon balance in the process, the contribution of autotrophic and heterotrophic organisms was also evaluated in terms of the influent NO2-N/NH4-N ratio (1:0.8 and 1:1.2 for Phase 1 and Phase 2, respectively). The result of this research demonstrates that the anaerobic ammonium removal from the piggery waste, using the UASB reactor, can be performed successfully. Furthermore, it appears that by using granular sludge as the seed biomass, the ANAMMOX reaction can start more quickly. Average nitrogen conversion was 0.59 kg T-N/m3 reactor-day (0.06 kg T-N/kg VSS/day) and 0.66 kg T-N/m3 reactor-day (0.08 kg T-N/kg VSS/day) for Phase 1 and Phase 2. The NO2-N/NH4-N removal ratio by the ANAMMOX was 1.48 and 1.79 for Phase 1 and Phase 2. The higher nitrite contents (about 50%) in the substrate resulted in higher nitrite nitrogen removal by the partial denitritation, as well as the ANAMMOX reaction, implying higher potential of partial denitritation. However, the result reveals that the ANAMMOX reaction was influenced less by the degree of partial denitritation, and the ANAMMOX bacteria did not compete with denitritation bacteria. The colour of the biomass at the bottom of the reactor changed from dark gray to dark red, which was accompanied by an increase in cytochrome content. At the end of the experiment, red-coloured granular sludge with diameter of 1-2 mm at the lower part of the reactor was also observed.     

Two-stage thermophilic-mesophilic anaerobic digestion of waste activated sludge from a biological nutrient removal plant.

A two-stage thermophilic-mesophilic anaerobic digestion pilot-plant was operated solely on waste activated sludge (WAS) from a biological nutrient removal (BNR) plant. The first-stage thermophilic reactor (HRT 2 days) was operated at 47, 54 and 60 degrees C. The second-stage mesophilic digester (HRT 15 days) was held at a constant temperature of 36-37 degrees C. For comparison with a single-stage mesophilic process, the mesophilic digester was also operated separately with an HRT of 17 days and temperature of 36-37 degrees C. The results showed a truly thermophilic stage (60 degrees C) was essential to achieve good WAS degradation. The lower thermophilic temperatures examined did not offer advantages over single-stage mesophilic treatment in terms of COD and VS removal. At a thermophilic temperature of 60 degrees C, the plant achieved 35% VS reduction, representing a 46% increase compared to the single-stage mesophilic digester. This is a significant level of degradation which could make such a process viable in situations where there is no primary sludge generated. The fate of the biologically stored phosphorus in this BNR sludge was also investigated. Over 80% of the incoming phosphorus remained bound up with the solids and was not released into solution during the WAS digestion. Therefore only a small fraction of phosphorus would be recycled to the main treatment plant with the dewatering stream.     

Fuzzy control of nitrogen removal in predenitrification process using ORP.

In order to meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of nitrogen from wastewater have to be implemented. In the past years, numerous studies have been carried out dealing with the application of fuzzy logic to improve the control of the activated sludge process. In this paper, fuzzy control strategies of predenitrification systems are presented that could lead to better effluent quality and, in parallel, to a reduction of chemicals consumption. Extensive experimental investigations on lab scale plant studies have shown that there was excellent correlation between nitrate concentration and ORP value at the end of the anoxic zone. Results indicated that ORP could be used as an on-line fuzzy control parameter of nitrate recirculation and external carbon addition. The optimal value of ORP to control nitrate recirculation and external carbon addition was - 86 +/- 2 mV and - 90 +/- 2 mV, respectively. The results obtained with real wastewater also showed the good performance and stability of the fuzzy controllers independently from external disturbances. The integrated control structure of nitrate recirculation and external carbon addition in the predenitrification system is also presented.     

Application of anaerobic biological treatment for sulphate removal in viscose industry wastewater.

Long term lab-scale and bench-scale experiments were performed to investigate the feasibility of the anaerobic process to treat wastewater from a pulp and viscose fibre industry. Anaerobic wastewater treatment enables an advantageous combination of COD, sulphate and zinc removal from viscose wastewater. The aim of the investigations was to evaluate the influence of the free sulphide concentration on COD and sulphate removal efficiency and on the substrate competition between sulphate reducing and methanogenic bacteria. Since the wastewater did not contain enough COD for complete sulphate removal it was of major interest to determine favourable process conditions to steer the substrate competition in favour of sulphate reduction. Further experiments at bench-scale permitted us to evaluate applicable COD-loading rates and gain fundamental information about process stability and optimization for large-scale implementation. The present work will deal with the most relevant experimental results achieved and with important technological aspects of anaerobic treatment of viscose wastewater.     

Biological nitrogen removal using bio-sorbed internal organic carbon from piggery wastewater in a post-denitrification MLE process.

Nitrogen removal from a piggery wastewater was investigated in a post-denitrification modified Lüdzack Ettinger (PDMLE) process. Overall hydraulic retention time (HRT) of the PDMLE, consisting of contact/separator (C/S), nitrification, denitrification and re-aerobic bioreactor was 10 days. 60% of the influent SCOD was separated in the C/S by contacting the return sludge with the synthetic wastewater, however, only 10% of the influent SCOD was separated from the piggery wastewater. Biosorption capacities of the synthetic wastewater and piggery wastewater were 800 and 150 mg/g-MLSS, respectively. In spite of the high organic and nitrogen load, nitrification efficiency was above 95%, and nitrification rate was about 180 mg-NH4+-N/L x day. The removed delta COD/delta nitrate ratios in the denitrification tank were 4.0 and 11.5 g-SCOD/g-nitrate, while denitrification rates were 8.4 and 2.6 mg-nitrate/day for synthetic and piggery wastewater, respectively. In the proposed PDMLE process, both bio-sorbed and bypassed organic matter could be successfully used for nitrate reduction as carbon sources and the final TN removal efficiency was as high as 95%.