Treatment of strong domestic sewage in a 96 m3 UASB reactor operated at ambient temperatures: two-stage versus single-stage reactor

A 96 m3 UASB reactor was operated for 2.5 years under different conditions to assess the feasibility of treating strong sewage (COD(tot) = 1531 mg/l) at ambient temperatures with averages of 18 and 25 degrees C for winter and summer respectively. During the first year, the reactor was operated as a two-stage system at OLRs in the range of 3.6-5.0 kg COD/m3 d for the first stage and 2.9-4.6 kg COD/m3 d for the second stage. The results of the first stage showed average removals of 51% and 60% for COD(tot) and COD(ss) respectively without significant effect of temperature. The second stage reactor was unstable. The temperature affected sludge stabilization. During the second year, the first stage was operated as a single-stage UASB reactor at half of the previous loading rates. The results showed an average removal efficiency of 62% for COD(tot) during summer, while it dropped to 51% during wintertime. However, the effluent suspended solids were stabilized with VSS/TSS ratio around 0.50 all over the year. The sludge in the single-stage reactor was well-stabilized and exerted an excellent settlability. During the last three months of research, sludge was discharged regularly from the single-stage UASB reactor. The results showed no significant improvement in the performance in terms of COD(tot). Based on the results of the experiment, a single-stage UASB reactor operated at relatively long HRT is preferred above two-stage system at the Jordanian conditions.     

The effect of pH on the efficiency of an SBR processing piggery wastewater

To treat piggery wastewater efficiently, the hydrolysis of urea (mainly derived from swine urine) in piggery wastewater with the change of sewage pH must be considered. Using activated sludge, piggery wastewater was treated in a sequencing batch reactor (SBR), and the effects of influent pH on SBR processing efficiency, sludge settle ability, and sludge activity were investigated. The results showed that a high influent pH value contributed to the improvement of the removal rate of ammonia nitrogen and reduction of the chemical oxygen demand (COD). When the influent pH was between 9.0 and 9.5, the removal rate of ammonia nitrogen was higher than 90%, and the reduction of COD from its original value was 80%. The influent pH had a greater influence on sludge concentration and sludge activity. When the influent pH increased from 7.0 to 9.5, the sludge concentration increased from 2,350 to 3,947 mg/L in the reactor, and the activities of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) first increased and then decreased. When the influent pH was 9.0 and 8.0, the maximum values (0.48 g O₂/(g MLSS/day) and 0.080 g O₂/(g MLSS/day)) were reached, and the sludge settling ratio was nearly steady between 20 and 35% in each reactor.     

Treatment of screened dairy manure by upflow anaerobic fixed bed reactors packed with waste tyre rubber and a combination of waste tyre rubber and zeolite: effect of the hydraulic retention time

Two laboratory-scale anaerobic fixed bed reactors were evaluated while treating dairy manure at upflow mode and semicontinuous feeding. One reactor was packed with a combination of waste tyre rubber and zeolite (R1) while the other had only waste tyre rubber as a microorganism immobilization support (R2). Effluent quality improved when the hydraulic retention time (HRT) increased from 1.0 to 5.5 days. Higher COD, BOD5, total and volatile solids removal efficiencies were always achieved in the reactor R1. No clogging was observed during the operation period. Methane yield was also a function of the HRT and of the type of support used, and was 12.5% and 40% higher in reactor R1 than in R2 for HRTs of 5.5 and 1.0 days, respectively. The results obtained demonstrated that this type of reactor is capable of operating with dairy manure at a HRT 5 times lower than that used in a conventional reactor.     

Nutrient removal from slaughterhouse wastewater in an intermittently aerated sequencing batch reactor

The performance of a 10 L sequencing batch reactor (SBR) treating slaughterhouse wastewater was examined at ambient temperature. The influent wastewater comprised 4672+/-952 mg chemical oxygen demand (COD)/L, 356+/-46 mg total nitrogen (TN)/L and 29+/-10 mg total phosphorus (TP)/L. The duration of a complete cycle was 8 h and comprised four phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactor was intermittently aerated with an air supply of 0.8L/min four times at 50-min intervals, 50 min each time. At an influent organic loading rate of 1.2g COD/(Ld), average effluent concentrations of COD, TN and TP were 150 mg/L, 15 mg/L and 0.8 mg/L, respectively. This represented COD, TN and TP removals of 96%, 96% and 99%, respectively. Phase studies show that biological phosphorus uptake occurred in the first aeration period and nitrogen removal took place in the following reaction time by means of partial nitrification and denitrification. The nitrogen balance analysis indicates that denitrification and biomass synthesis contributed to 66% and 34% of TN removed, respectively.     

Performance of anaerobic contact filter in series for treating distillery spentwash

Investigations were carried out by using rigid polyurethane foam as a packing material in the anaerobic contact filter (series) to treat distillery spentwash. The effect of hydraulic retention time (HRT) in treatment efficiency of reactor (I) and (II) was evaluated at different initial substrate concentrations ranging from 1500 mg/l to 19,000 mg/l. The effect of toxic parameters such as sulphate present in the distillery spentwash and the corresponding parameters such as total sulphide and un-ionized hydrogen sulphide generated during digestion of wastewater were evaluated to assess the reactor performance. The results showed that at 4 d HRT the overall COD removal percent ranged from 98% to 73% for an influent COD of 1500 mg/l to 19,000 mg/l. The overall performance of COD removal percent in reactor (I) and (II) at 2, 3 and 4 d HRT's were investigated. At 3 d HRT the reactor (II) showed a higher COD removal percent when compared to reactor (I), which clearly shows the role of hydraulic retention time in degradation of the organic matter present in the wastewater above an influent COD concentration of 5000 mg/l.     

Ambient temperature treatment of low strength wastewater using anaerobic sequencing batch reactor

Low strength wastewater having chemical oxygen demands (COD) concentrations of 1000, 800, 600 and 400mg/l were treated at 35, 25, 20 and 15¡C using four anaerobic sequencing batch reactors (ASBRs). Reactor 1 was operated at hydraulic retention time (HRT) of 48h, reactor 2 at 24h HRT, reactor 3 at 16h HRT and reactor 4 at 12h HRT. 80 to 99% soluble COD was removed at the various operational conditions, except during 15¡C treatment of 1000 and 800mg/l COD wastewater at 12h HRT and 1000mg/l COD wastewater at 16h HRT, where excessive loss of biological solids occurred. The ASBR process can be an effective process for the treatment of low concentrated wastewaters which are usually treated aerobically with large amount of sludge production and higher energy expenditures.     

Volatile fatty acids production from food wastes and its application to biological nutrient removal

Korean food wastes were anaerobically digested to produce volatile fatty acids (VFA) that can be used as a carbon source in biological nutrient removal in a sequential batch reactor (SBR). Acetate, propionate and butyrate were produced at a yield of 379-400 g VFA/kg VS₀ (initial volatile solids). The ratio of SCOD (Soluble Chemical Oxygen Demand) of VFA to ammonia nitrogen (N) was in the range of 36.2-36.5 and the ratio of SCOD to phosphorus was between 151 and 162. The removal rate of nitrogen and phosphorus improved from 44% and 37% to 92% and 73%, respectively when the VFA were added to the influent of the Taejon municipal wastewater plant. The concentration of nitrogen and phosphorus were maintained below 3 mg/l and 1 mg/l, respectively. The N- and P-content of the food waste was low enough not to influence the final N- and P-concentrations of the wastewater.     

Development of an improved anaerobic filter for municipal wastewater treatment

Development of an improved reactor configuration of anaerobic filter was carried out for the elimination of clogging of filter media. The experiments over different hydraulic retention times (HRTs) indicated that the HRT of 12 h was the most appropriate one for the system studied while treating the municipal wastewater, which resulted 90% and 95% BOD and COD reduction, respectively. Reduction up to 95% in suspended solids concentration could be achieved without any pretreatment. The specific biogas yield obtained was 0.35 m(3) CH(4)/kgCODr with 70% of CH(4) content in the biogas generated from the system at the HRT of 12 h. Operational problems such as clogging of filter media were not observed throughout the period of study over 600 d.     

Anaerobic treatment of low-strength municipal wastewater by a two-stage pilot plant under psychrophilic conditions

A two-stage anaerobic treatment pilot plant was tested for the treatment of raw domestic wastewater under temperatures ranging from 21 to 14 degrees C. The plant consisted of a hydrolytic upflow sludge bed (HUSB) digester (25.5m3) followed by an upflow anaerobic sludge blanket (UASB) digester (20.36m3). The hydraulic retention time (HRT) varied from 5.7 to 2.8h for the first stage (HUSB digester) and from 13.9 to 6.5h for the second stage (UASB digester). Total suspended solids (TSS), total chemical oxygen demand (TCOD), and biochemical oxygen demand (BOD) removals ranged from 76% to 89%, from 49% to 65%, and from 50% to 77%, respectively, for the overall system. The percentage of influent COD converted to methane was 36.1%, the hydrolysis of influent volatile suspended solids (VSS) reached 59.7% and excess biomass was 21.6% of the incoming VSS. Plant performance was influenced by the wastewater concentration and temperature, yet better results were obtained for influent COD higher than 250mg/l.     

Effect of COD/N ratio on cultivation of aerobic granular sludge in a pilot-scale sequencing batch reactor

Aerobic granular sludge was successfully cultivated with the effluent of internal circulation reactor in a pilot-scale sequencing batch reactor (SBR). Soy protein wastewater was used as an external carbon source for altering the influent chemical oxygen demand/nitrogen (COD/N) ratios of SBR. Initially, the phenomenon of partial nitrification was observed and depressed by increasing the influent COD/N ratios from 3.32 to 7.24 mg/mg. After 90 days of aerobic granulation, the mixed liquor suspended solids concentration of the reactor increased from 2.80 to 7.02 g/L, while the sludge volumetric index decreased from 105.51 to 42.99 mL/g. The diameters of mature aerobic granules vary in the range of 1.2 to 2.0 mm. The reactor showed excellent removal performances for COD and $ {\text{NH}}_4^{ + }{\text{ - N}} $ after aerobic granulation, and average removal efficiencies were over 93% and 98%, respectively. The result of this study could provide further information on the development of aerobic granule-based system for full-scale applications.     

Statistical modeling and optimization of biomass granulation and COD removal in UASB reactors treating low strength wastewaters

The aim of this work was to study the influence of influent chemical oxygen demand (COD), upflow velocity of wastewater, and cationic polymer additives in inoculum, on biomass granulation and COD removal efficiency in upflow anaerobic sludge blanket (UASB) reactor for treating low strength wastewater. Statistical models were formulated based on these three variables to optimize the biomass granulation and COD removal efficiency in UASB reactors using a two-level, full factorial design. For the thick inoculum used in this study, having suspended solids (SS) >80 g/l and volatile suspended solids (VSS) to SS ratio <0.3, cationic polymer additives in the inoculum showed adverse effect on biomass granulation and COD removal efficiency. It is concluded that for such thick inoculum, granulation can be obtained while treating low strength wastewaters in UASB reactor by selecting proper combination of influent COD and liquid upflow velocity so as to represent the organic loading rate (OLR) greater than 1.0 kg COD/m(3) d. Validation of model predictions for treatment of synthetic wastewater and actual sewage reveals the efficacy of these models for enhancing granulation and COD removal efficiency.     

Continuous fill intermittent decant type sequencing batch reactor application to upgrade the UASB treated sewage

The performance of continuous flow intermittent decant type sequencing batch (CFID) reactor treating the effluent of an UASB reactor treating domestic wastewater and operated at 8 h hydraulic retention time (HRT) was investigated. The CFID was operated at three different HRTs (22, 8 and 6 h) and three different dissolved oxygen (DO) patterns (<0.5, 2.5–3.5 and 3.5–4.5 mg/L). The highest effluent quality was observed at the 8 h HRT and 2.5–3.5 mg/L DO concentration. At this operational condition, the average BOD, TSS, ammonia nitrogen and fecal coliform removal efficiencies were 83, 90, 74 and 99 %, respectively. The CFID is a promising post-treatment option for existing UASB systems, with a final effluent quality that comply with receiving water and effluent reuse criteria.     

Nitrification,denitrification and biological phosphorus removal in piggery wastewater using a sequencing batch reactor

Nutrients in piggery wastewater with high organic matter, nitrogen (N) and phosphorus (P) content were biologically removed in a sequencing batch reactor (SBR) with anaerobic, aerobic and anoxic stages. The SBR was operated with 3 cycles/day, temperature 30 degrees C, sludge retention time (SRT) 1 day and hydraulic retention time (HRT) 11 days. With a wastewater containing 1500 mg/l ammonium and 144 mg/l phosphate, a removal efficiency of 99.7% for nitrogen and 97.3% for phosphate was obtained. Experiments set up to evaluate the effect of temperature on the process showed that it should be run at temperatures higher than 16 degrees C to obtain good removals (> 95%). Batch tests (ammonia utilization rate, nitrogen utilization rate and oxygen utilization rate) proved to be good tools to evaluate heterotrophic and autotrophic biomass activity. The SBR proved to be a very flexible tool, and was particularly suitable for the treatment of piggery wastewater, characterized by high nutrient content and by frequent changes in composition and therefore affecting process conditions.     

Effects of pH adjustment by parawood ash and effluent recycle ratio on the performance of anaerobic baffled reactors treating high sulfate wastewater

The objective of this study was to compare the performance of anaerobic baffled reactor (ABR) treating concentrated rubber latex wastewater under different pH adjustment substances and recycling ratios (R). Two ABRs, one received wastewater pretreated with NaOH and the other with ash, were operated at 35 degrees C under identical HRTs from 10 to 1.25d. Results show that both ABRs had highest COD and sulfate removal efficiencies at HRT 10d (averaged 82.71% and 96.16% of ABR-NaOH, and 80.77% and 96.60% of ABR-Ash, respectively), where majority of the influent COD and sulfate were removed by the first compartment of the ABR at all conditions tested. Increasing R (0, 0.3 and 0.5) raised the hydraulic loading on the system and resulted in a drop of organic removal efficiency and methane yield. Translocation of sulfate reducing bacteria and methanogens in the ABRs caused by increased organic loading and effluent recycle is discussed. The results show great potential of parawood ash as a pH adjustment substance for acidic wastewaters.     

Lab-scale study of an anaerobic membrane bioreactor (AnMBR) for dilute municipal wastewater treatment

Anaerobic bioreactors supplemented with membrane technology have become quite popular, owing to their favorable energy recovery characteristics. In this study, a lab-scale anaerobic Membrane Bioreactor (AnMBR) was assessed in experimental treatments of pre-settled dilute municipal wastewater obtained from a full-scaled wastewater treatment plant. The MBR system was operated in continuous flow mode for 440 days. To evaluate the performance of the AnMBR under various loading rates, the hydraulic retention time (HRT) was reduced in a stepwise manner (from 2 to 0.5 days). Afterward, the mixed liquor suspended solids (MLSS) were reduced from 7,000 to 3,000 mg/L in increments of 1,000 mg/L, resulting in a decrease in solids retention time (SRT) at a constant HRT of 1.0 day. The soluble chemical oxygen demand (SCOD) concentration in the feed varied between 38 and 131 mg/L, whereas the average permeate SCOD ranged between 18 and 37 mg/L, reflecting excellent effluent quality. The AnMBR performance in terms of COD removal proved stable, despite variations in influent characteristics and HRT and SRT changes. The concentration of extracellular polymeric substance (EPS) was reduced with decreases in HRT from 42 to 22 mg VS/mg of MLSS, thereby indicating that the increased biomass concentration biodegraded the EPS at lower HRTs. AnMBR is, therefore, demonstrably a feasible option for the treatment of dilute wastewater with separate stage nitrogen and phosphorus removal processes.     

Advanced monitoring and supervision of biological treatment of complex dairy effluents in a full-scale plant

The operation of a wastewater treatment plant treating effluents from a dairy laboratory was monitored by an advanced system. This plant comprises a 12 m(3) anaerobic filter (AF) reactor and a 28 m(3) sequential batch reactor (SBR) coupled in series and is equipped with the following on-line measurement devices: biogas flow meter, feed and recycling flow meters, temperature sensor, dissolved oxygen analyzer, and redox meter. Other parameters such as chemical oxygen demand (COD), volatile fatty acids (VFA), etc. were determined off-line. The plant has been in operation for 634 days, the influent flow rate being 6-8 m(3)/d. COD concentration of the influent ranged between 8 and 12 kg COD/m(3), resulting in COD values in the effluent around 50-200 mg/L. The behavior of the system was studied using the set of measurements collected by the data acquisition program especially developed for this purpose. Monitoring of variables such as anaerobic reactor temperature permitted the detection and prevention of several failures such as temperature shocks in the AF reactor. Besides, off-line measurements such as the alkalinity or the VFA content, together with the on-line measurements, provided immediate information about the state of the plant and the detection of several anomalies, such as organic overloads in the SBR, allowing the implementation of several fast control actions.     

A novel process configuration for anaerobic digestion of source-sorted household waste using hyper-thermophilic post-treatment

A novel reactor configuration was investigated for anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). An anaerobic hyper-thermophilic (68 degrees C) reactor R68 was implemented as a post-treatment step for the effluent of a thermophilic reactor R1 (55 degrees C) in order to enhance hydrolysis of recalcitrant organic matter, improve sanitation and ease the stripping of ammonia from the reactor. The efficiency of the combined system was studied in terms of methane yield, volatile solids (VS) reduction, and volatile fatty acid (VFA) production at different hydraulic retention times (HRT). A single-stage thermophilic (55 degrees C) reactor R2 was used as control. VS reduction and biogas yield of the combined system was 78-89% and 640-790 mL/g VS, respectively. While the VS reduction in the combined system was up to 7% higher than in the single-stage treatment, no increase in methane yield was observed. Shifting the HRT of the hyper-thermophilic reactor from 5 days to 3 days resulted in a drop in the methanogenic activity in the hydrolysis reactor to a minimum. Operation of R68 at HRTs of 24-48 h was sufficient to achieve high VS conversion into VFAs. Removal of pathogens was enhanced by the hyper-thermophilic post-treatment. 7% of the ammonia load was removed in the hyper-thermophilic reactor with a flow of headspace gas through the reactor equivalent to four times the biogas flow produced in reactor R1.     

Biomethanation of poultry litter leachate in UASB reactor coupled with ammonia stripper for enhancement of overall performance

In the present study possibility of coupling stripper to remove ammonia to the UASB reactor treating poultry litter leachate was studied to enhance the overall performance of the reactor. UASB reactor with stripper as ammonia inhibition control mechanism exhibited better performance in terms of COD reduction (96%), methane yield (0.26m(3)CH(4)/kg COD reduced), organic loading rate (OLR) (18.5kg COD m(-3)day(-1)) and Hydraulic residence time (HRT) (12h) compared to the UASB reactor without stripper (COD reduction: 92%; methane yield: 0.21m(3)CH(4)/kg COD reduced; OLR: 13.6kg CODm(-3)day(-1); HRT: 16h). The improved performance was due to the reduction of total ammonia nitrogen (TAN) and free ammonia nitrogen (FAN) in the range of 75-95% and 80-95%, respectively by the use of stripper. G/L (air flow rate/poultry leachate flow rate) in the range of 60-70 and HRT in the range of 7-9min are found to be optimum parameters for the operation of the stripper.     

Anaerobic co-digestion of olive mill wastewater with olive mill solid waste in a tubular digester at mesophilic temperature

Anaerobic co-digestion is a well established process for treating many types of organic wastes, both solid and liquid. In this study we have investigated, on a laboratory scale, the anaerobic co-digestion of olive mill wastewater (OMW) with olive mill solid waste (OMSW) using semi-continuous, feeding, tubular digesters operated at mesophilic temperatures. Each digester was fed with an influent, composed of OMW and OMSW, at an organic loading rate (OLR) varying between 0.67 and 6.67 g COD/l/d. The hydraulic retention times (HRT) were 12, 24 and 36 days. The TCOD concentrations of OMW used as the main substrate were 24, 56 and 80 g COD/l; the amount of the dry OMSW used as a co-substrate was fixed to approximately 56 g/l of OMW. The results indicated that the best methane production was about 0.95 l/l/day obtained at an OLR = 4.67 g COD/l/d, corresponding to influent TCOD = 56 g COD/l at an HRT = 12d. In contrast, the maximum TCOD removal efficiency (89%) was achieved at an OLR = 0.67 g COD/l/d, corresponding to influent TCOD = 24 g COD/l at an HRT = 36 d. Moreover, the inhibition of biogas production was observed at the highest OLR studied.     

Integration of a Coagulation/Flocculation step in a biological sequencing batch reactor for COD and nitrogen removal of supernatant of anaerobically digested piggery wastewater

The supernatant from mesophilic anaerobic digestion of piggery wastewater is characterised by a high amount of COD (4.1 g COD L(-1)), ammonium (2.3g NH(4)(+)-NL(-1)) and suspended solids (2.5 g SS L(-1)). This effluent can be efficiently treated by means of a Sequencing Batch Reactor (SBR) strategy for biological COD, SS and nitrogen removal including a Coagulation/Flocculation step. Total COD and SS reduction yields higher than 66% and 74%, respectively, and a total nitrogen removal (via nitrite) of more than 98% were reached when working with HRT 2.7 days, SRT 12 days, temperature 32 degrees C, three aerobic/anoxic periods, without external control of pH and under limited aeration flow. The inhibition of nitrite oxidizing biomass was achieved by the working free ammonia concentration and the restricted air supply (dissolved oxygen concentration below 1 mg O(2)L(-1)). Since a part of the total COD was colloidal and/or refractory, a Coagulation/Flocculation step was implemented inside the SBR operating strategy to meet a suitable effluent quality to be discharged. Several Jar-Tests demonstrated that the optimal concentration of FeCl(3) was 800 mg L(-1). A respirometric assay showed that this coagulant dosage did not affect the biological activity of nitrifying/denitrifying biomass.