Low COD Research Articles

Influence of hydraulic retention time on the operation of a submerged membrane sequencing batch reactor (SM-SBR) for the treatment of greywater

This study describes the experience received in operating an SM-SBR under different hydraulic retention times for the treatment of synthetic greywater. The pilot scale SM-SBR with a working volume of VR = 500 L is operated with hydraulic retention times of 33, 24 and 12 h, and a volumetric exchange ratio of ~0.25. The removal of COD, ammonia, total nitrogen is investigated for the different set-ups. Despite the low COD in greywater, the treatment performance of the reactor is always sufficient to meet reuse guidelines. The biomass concentration increases slowly, although no excess sludge has been taken out (except sampling). Therefore, the sludge age is assumed to be >360 d.

Landfill leachate treatment by electrochemical oxidation

This study investigated the electrochemical oxidation of stabilized leachate from Pulau Burung semi-aerobic sanitary landfill by conducting laboratory experiments with sodium sulfate Na(2)SO(4) (as electrolyte) and graphite carbon electrodes. The control parameters were influent COD, current density and reaction time, while the responses were BOD removal, COD removal, BOD:COD ratio, color and pH. Na(2)SO(4) concentration was 1 g/L. Experiments were conducted based on a three-level factorial design and response surface methodology (RSM) was used to analyze the results. The optimum conditions were obtained as 1414 mg/L influent COD concentration, 79.9 mA/cm(2) current density and 4 h reaction time. This resulted in 70% BOD removal, 68% COD removal, 84% color removal, 0.04 BOD/COD ratio and 9.1 pH. Electrochemical treatment using graphite carbon electrode was found to be effective in BOD, COD and color removal but was not effective in increasing the BOD/COD ratio or enhancing biodegradability of the leachate. The color intensity of the treated samples increased at low influent COD and high current density due to corrosion of electrode material.

Stability and efficiency of biofilms for landfill leachate treatment

The objective of this work was to assess the feasibility of a fixed-film biological aerated filtration process for the treatment of the leachate produced at Harnhill landfill site (South Gloucestershire, UK). The laboratory scale plant consisted of four identical biological aerated filters (a triplicate and a “control” column) packed with small brick fragments. Biofilm formed within 24 h of immersion of the support material in the reactor, and had a high resistance to antibiotics and other toxic agents. The plant maintained a stable operation in the 20–45 °C temperature range, showing the best results (35.4 ± 6.6% COD removal and 73.9 ± 5.5% BOD 5 reduction) at 40 °C. The lowest COD and BOD 5 values obtained at the outlet of the columns were 7067 mg/L and 1050 mg/L, respectively.

Upflow anaerobic clarification tank (UACT) to upgrade existing anaerobic effluents

The Upflow Anaerobic Clarification Tank (UACT) is of interest as a post-treatment step for high-rate anaerobic wastewater treatment systems. The UACT contributes to extra capture of methane from the raw wastewater. It also significantly facilitates the reuse of the treated water. The efficiency of the UACT process is demonstrated in this study using laboratory-scale reactors. The water produced by the UACT had a low total COD, in most cases below 145 mg/L and a soluble COD below 60 mg/L at surface loading rates between 0.1-0.4 m(3)/(m(2) h) and hydraulic retention times between 5-6 h. The sludge bed of the UACT was characterised by 6-10 times higher substrate affinity (for ethanol, acetate and propionate) compared to the parent UASB and similar specific activity. The results suggest that a UASB followed by the UACT can, upon subsequent application of a rapid filtration, qualify as a total COD removal, no longer necessitating aerobic treatment.

Identification of dominant microbial community in aerophilic biofilm reactors by fluorescence in situ hybridization and PCR-denaturing gradient gel electrophoresis

This study was conducted by combining fluorescence in situ hybridization (FISH) performed on 16S rRNA and polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) with 16S CTOs primers to characterize the nitrifying microbial communities in biofilm processes, which were tested to retrofit the S municipal wastewater treatment plant in Busan, Korea. Four aerophilic biofilm reactors were operated with hydraulic retention times of 2 to 8 h and biofilms were grown on ceramic media. The same low COD/ NH 4 + -N ratio (100 mg/L of COD over 40 mg/L of NH 4 + -N) with the S plant was used. The average relative population ratios of Nitrosomonas spp. to ammonia oxidizing bacteria (AOB) as measured by specific FISH probes (%/Nso190) were 75.0%, 80.0%, 73.0% and 73.5%, respectively, while those of Nitrosospira spp. to AOB were 21.0%, 14.7%, 24.6% and 24.1% after 180 days of operation. The microbial composition of Nitrobacter spp. detected by using a Nit3 probe was below 10% in each reactor. In contrast, Nitrospira genus detected with an Ntspa662 probe was around 20%. When CTOs primer was applied in PCR-DGGE analysis to define the nitrifying bacteria, the bands of group B in the R-1 reactor with the highest hydraulic retention time (HRT) had the strongest light intensity compared with two other reactors with lower HRTs after day 64. The bands of the groups were responsible for nitrification with the major dominant population in each reactor depending on the change of ammonia removal rate. These results would directly lead to an understanding of the reactor performance in relation to the ammonia removal, when conventional municipal wastewater treatment plants are retrofitted or upgraded to biological nitrogen removal processes using biofilm.

Effects of Upflow Liquid Velocity on Performance of Expanded Granular Sludge Bed (EGSB) System

� Abstract—The effects of upflow liquid velocity (ULV) on performance of expanded granular sludge bed (EGSB) system were investigated. The EGSB reactor, made from galvanized steel pipe 0.10 m diameter and 5 m height, had been used to treat piggery wastewater, after passing through acidification tank. It consisted of 39.3 l working volume in reaction zone and 122 l working volume in sedimentation zone, at the upper part. The reactor was seeded with anaerobically digested sludge and operated at the ULVs of 4, 8, 12 and 16 m/h, consecutively, corresponding to organic loading rates of 9.6 - 13.0 kg COD/ (m 3 od). The average COD concentrations in the influent were 9,601 - 13,050 mg/l. The COD removal was not significantly different, i.e. 93.0% - 94.0%, except at ULV 12 m/h where SS in the influent was exceptionally high so that VSS washout had occurred, leading to low COD removal. The FCOD and VFA concentrations in the effluent of all experiments were not much different, indicating the same range of treatment performance. The biogas production decreased at higher ULV and ULV of 4 m/h is suggested as design criterion for EGSB system.

Assessment of olive-mill wastewater as a growth medium for lipase production by Candida cylindracea in bench-top reactor

Olive-mill wastewater (OMW) was investigated for its suitability to serve as a medium for lipase production by Candida cylindracea NRRL Y-17506. The OMW that best supported enzyme production was characterized by low COD and low total sugars content. In shake flask batch cultures, OMW supplementation with 2.4 g l −1 NH 4Cl and 3 g l −1 olive oil led to an enzyme activity of about 10 U ml −1. The addition of glucose or malt extract and supplements containing organic N (e.g., peptone, yeast extract) either depressed or did not affect the enzyme production. Further experiments were then performed in a 3-l stirred tank reactor to assess the impact of medium pH and stirring speed on the yeast enzyme activity. The lipase activity was low (1.8 U ml −1) when the pH was held constant at 6.5, significantly increased (18.7 U ml −1) with uncontrolled pH and was maximum (20.4 U ml −1) when the pH was let free to vary below 6.5. A stirring regime, that varied depending on the dissolved oxygen concentration in the medium, both prevented the occurrence of anoxic conditions during the exponential growth phase and enabled good lipase production (i.e., 21.6 U ml −1) and mean volumetric productivity (i.e., 123.5 U l −1 h −1).

In situ microbial treatment of landfill leachate using aerated lagoons

The aim of this study was to assess the efficiency of leachate treatment by microbial oxidation in four connected on-site aerated lagoons at a landfill site. The landfill site was found to be in an ageing methanogenic state, producing leachate with relatively low COD (mean value 1740 mg l −1) and relatively high ammonium concentrations (mean value 1241 mg l −1). Removal of COD averaged 75%, with retention times varying from 11 to 254 days. Overall 80% of the N load was removed within the plant, some by volatilisation of ammonium. Microbial community profiling of the water from each lagoon showed a divergent community profile, presumably a reflection of the nutrient status in each lagoon. In municipal solid waste landfills under similar conditions, leachate treatment through a facultative aerobic system in which sequential aerobic and anaerobic microbial oxidations occurred can readily be achieved using a simple two-lagoon system, suggesting this technology can be economic to install and simple to run.

Characterisation and treatment of leachates from the municipal sanitary landfill of Thessaloniki, Greece

The optimum treatment technologies of leachates produced from a municipal landfill were studied in this work. Leachates composition ranged from high-strength acidic down to low-strength stabilised leachates, affecting the applicable treatment process. Efficient treatment of fresh leachates was achieved by biological methods, such as the SBR, or the moving bed processes, resulting in increased removal of organic and nitrogen content. However, biological methods were not effective for the treatment of stabilised leachates, containing non-biodegradable compound; physical-chemical methods were proved to be more efficient. The combination of coagulation/flocculation followed by ozonation was an efficient technique, with low effluent COD values, <180 mg/L.

Denitrifying phosphorus removal in a step-feed CAST with alternating anoxic-oxic operational strategy

A bench-scale cyclic activated sludge technology (CAST) was operated to study the biological phosphorus removal performance and a series of batch tests was carried out to demonstrate the accumulation of denitrifying polyphosphate-accumulating organisms (DNPAOs) in CAST system. Under all operating conditions, step-feed CAST with enough carbon sources in influent had the highest nitrogen and phosphorus removal efficiency as well as good sludge settling performance. The average removal rate of COD, NH4+-N, PO4(3-)-P and total nitrogen (TN) was 88.2%, 98.7%, 97.5% and 92.1%, respectively. The average sludge volume index (SVI) was 133 mL/g. The optimum anaerobic/aerobic/anoxic (AOA) conditions for the cultivation of DNPAOs could be achieved by alternating anoxic/oxic operational strategy, thus a significant denitrifying phosphorus removal occurred in step-feed CAST. The denitrification of NOx(-)-N completed quickly due to step-feed operation and enough carbon sources, which could enhance phosphorus release and further phosphorus uptake capability of the system. Batch tests also proved that polyphosphate-accumulating organisms (PAOs) in the step-feed process had strong denitrifying phosphorus removal capacity. Both nitrate and nitrite could be used as electron acceptors in denitrifying phosphorus removal. Low COD supply with step-feed operation strategy would favor DNPAOs accumulation.

Biodegradation of 2,4,6-trinitrophenol (picric acid) in a biological aerated filter (BAF)

This study demonstrated the microbial purification of a model wastewater containing 2,4,6-trinitrophenol (TNP), which was carried out in a continuously working biological aerated filter (BAF). The main emphasis was on the operating performance of the reactor as a function of the pollution load. TNP was degraded at a maximum volumetric removal rate of 2.53 g TNP/L d, with low residual COD and TNP concentration. Overloading of TNP inhibited the nitrite-oxidizing activity, resulting in poor TNP degradation performance in the BAF system. The inhibition depended on some factors, such as influent concentrations and flow rates of the influent. It is assumed that nitrite-oxidizing occurred spontaneously during TNP degradation in the BAF system, could have significant influence on TNP wastewater treatment. One year after the reactor start-up, the dominance of Rhodococcus, which was initially inoculated in the reactor, was confirmed by analysis of 16S rDNA sequence of the PCR products separated by DGGE.

2,4-Dichlorophenol (DCP) containing wastewater treatment using a hybrid-loop bioreactor

Synthetic wastewater containing 2,4-dichlorophenol (DCP) was biologically treated using a hybrid-loop bioreactor system consisting of a packed column biofilm reactor (PCBR) and an aerated tank with effluent recycle. Effects of the feed DCP concentration on COD, DCP and toxicity removals were investigated. Biomass concentration in the packed column and in the aeration tank decreased with increasing feed DCP content due to toxic effects of DCP on the microorganisms. Low biomass concentrations at high DCP contents resulted in low COD, DCP and toxicity removals. Therefore, percent DCP, COD and toxicity removals decreased with increasing feed DCP content. Nearly 70% COD removal was achieved with a feed DCP content of 380 mg L −1. The system should be operated with the feed DCP lower than 100 mg L −1 in order to obtain DCP, COD and toxicity removals above 90%.

The effect of flow equalisation and prefermentation on the sludge production and sludge characteristics in a BNR plant

A full-scale study investigated the influence of diurnal flow equalisation and prefermentation on the characteristics of sludge. The diurnal variations in the sludge concentration and the level of sludge blanket in the secondary clarifiers were evened out significantly with the use of an equalization basin. Stable conditions in the aeration basin and in the secondary clarifiers contributed to the improvements in the performance of the BNR plant. A decrease in the waste activated sludge production and an improvement in the settleability were also observed. The low WAS yield was attributed to the low yield COD compounds produced by the prefermentation, longer sludge age and constant conditions obtained by the flow equalisation. Some evidence was found that good settling properties would be related to the amount of suspended solids fed to the biological process as well as to the good performance of the biological process.

Denitrification of wastewater containing high nitrate and calcium concentrations

The removal of nitrate from rinse wastewater generated in the stainless steel manufacturing process by denitrification in a sequential batch reactor (SBR) was studied. Two different inocula from wastewater treatment plants were tested. The use of an inoculum previously acclimated to high nitrate concentrations led to complete denitrification in 6 h (denitrification rate: 22.8 mg NO 3 - -N / g VSS h ), using methanol as carbon source for a COD/N ratio of 4 and for a content of calcium in the wastewater of 150 mg/L. Higher calcium concentrations led to a decrease in the biomass growth rate and in the denitrification rate. The optimum COD/N ratio was found to be 3.4, achieving 98% nitrate removal in 7 h at a maximum rate of 30.4 mg NO 3 - -N / g VSS h and very low residual COD in the effluent.

Cod bycatch in otter trawls and in longlines with different bait types in the Georges Bank haddock fishery

In the Northwest Atlantic, bycatch of depleted groundfish stocks in the haddock fishery on Georges Bank is an ongoing concern. In recent years, this fishery on the American side of Georges Bank has been limited by high bycatch rates of cod. Considerable conservation engineering work has been done to address the problem, including experiments with different longline baits and modifications to otter trawl gear. Fabricated baits have shown promise for increased selectivity when longlining, but it has sometimes been difficult to establish whether low cod catch rates with fabricated baits have resulted from bait selectivity or from a low abundance of cod in the area. In this study, we compare catch rates of cod and haddock between otter trawls and longline gear in experimental and commercial fishing on Georges Bank in the summer of 2005. We also compare cod bycatch rates among longlines baited with squid, herring, or fabricated baits (mainly Norbait 700E) in Georges Bank Closed Area 1, from October 2003 to June 2005. Records from the Northeast Fisheries Observer Program were combined with data collected by the Cape Cod Commercial Hook Fishermen's Association (CCCHFA), and compared using generalized linear models. In the Eastern US-Canada Resource Sharing Area (EUSCA) in the summer of 2005 catch of cod per haddock by weight was significantly lower when fishing with longline gear (0.008–0.045 kg cod per kg haddock) than with otter trawl gear (0.059–0.826 kg cod per kg haddock), in all months and areas. Cod bycatch rates were also significantly lower for longlines fishing for haddock than for otter trawls fishing for groundfish species other than haddock. In Closed Area 1, statistically significant differences in cod to haddock ratios were found between baits, with squid catching the highest amount of cod, fabricated baits catching the lowest amount, and herring at an intermediate level. The development of fishing methods that minimize cod bycatch is a high priority in many regions of the North Atlantic. These results indicate that longlines with fabricated bait have the potential to maintain a very low catch of cod while fishing for haddock.

Biological treatment of 2,4,6-trichlorophenol (TCP) containing wastewater in a hybrid bioreactor system with effluent recycle

Due to the toxic effects of trichlorophenol (TCP) on microorganisms, biological treatment efficiencies of TCP containing wastewaters are usually low. Synthetic wastewater containing 2,4,6-TCP was biologically treated in a hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with effluent recycle in order to improve COD and TCP removals. Effects of the feed TCP concentration on COD, TCP and toxicity removal performance of the system were investigated for the feed TCP between 50 and 450 mg L −1 while the sludge age (solids retention time, SRT) and hydraulic residence time (HRT) were kept constant at 20 d and 25 h, respectively. Biomass concentrations in the packed column and in the aeration tank decreased with increasing feed TCP concentrations due to toxic effects of TCP on the organisms. Low biomass concentrations in the system at high feed TCP contents resulted in low COD, TCP and toxicity removals. Therefore, percent TCP, COD and toxicity removals decreased with increasing feed TCP concentrations especially above 400 mg L −1. The effluent TCP concentrations were lower than 20 mg L −1 for the feed TCP concentrations below 390 mg L −1 resulting in TCP and COD removals above 90%. Specific rates of TCP and COD removals increased with the feed TCP due to low biomass concentrations at high TCP contents. The system should be operated at a feed TCP lower than 400 mg L −1 in order to obtain more than 90% TCP, COD and toxicity removals under the specified experimental conditions.

The effect of landfill age on municipal leachate composition

The influence of municipal landfill age on temporal changes in municipal leachate quality on the basis of elaboration of 4 years monitoring of leachate from landfill in Wysieka near Bartoszyce (Poland) is presented in this study. In leachate, concentrations of organic compounds (COD, BOD 5), nutrients (nitrogen, phosphorus), mineral compounds, heavy metals and BTEX were investigated. It was shown that the principal pollutants in leachate were organics and ammonia – as landfill age increased, organics concentration (COD) in leachate decreased from 1800 mg COD/l in the second year of landfill exploitation to 610 mg COD/l in the sixth year of exploitation and increase of ammonia nitrogen concentration from 98 mg N NH 4 /l to 364 mg N NH 4 /l was observed. Fluctuation of other indexes (phosphorus, chlorides, calcium, magnesium, sulfate, dissolved solids, heavy metals, BTEX) depended rather on season of the year (seasonal variations) than landfill age. Moreover, the obtained data indicate that despite of short landfill’s lifetime some parameters e.g. high pH (on average 7.84), low COD concentration (<2000 mg COD/l), low BOD 5/COD ratio (<0.4) and low heavy metal concentration, indicated that the landfill was characterized by methanogenic conditions already at the beginning of the monitoring period.

Flux and performance improvement in a submerged anaerobic membrane bioreactor (SAMBR) using powdered activated carbon (PAC)

A three litre submerged anaerobic membrane bioreactor (SAMBR) was used to examine the effect of powdered activated carbon (PAC) on COD removal and flux. 98% COD removal efficiency was achieved at a high loading rate (16 gCOD l −1 d −1) and a low hydraulic retention time (HRT) of 6 h in the presence of 3.4 g l −1 of PAC. PAC addition improved start-up and performance during a hydraulic shock by buffering the volatile fatty acids (VFAs), however, a large amount of biomass was important in accommodating the higher loading rate in the SAMBR. Batch assays showed that PAC addition improved methane potential both in terms of amount and inoculation time. COD retention inside the SAMBR for three experiments was proportional to the soluble microbial products (SMPs) contribution to COD, as (VFAs) passed through the membrane at high sparging rates (5 litres per minute—LPM). Size exclusion chromatography showed that the membrane acted as an ultra-filter (<30 kDa) as the cake or gel layer significantly reduced the amount of organics passing through the membrane. PAC adsorbed slowly biodegradable low and high MW residual COD from the bulk liquid, and hence improved COD removal and flux. Particle size distributions demonstrated that PAC also adsorbs fine colloids, and flux data showed that only a thin biofilm was formed due to the high backtransport velocity of PAC. The combined effects of adsorption of fine colloids and dissolved organics, and the formation of a thin cake layer resulted in significant flux improvement from 2 to 9 litres per square metre per hour (LMH) in the presence of 1.67 g l −1 PAC. However, addition of 3.4 g l −1 PAC reduced the flux to 5 LMH by the combined effect of viscosity and its inability to completely adsorb the dissolved organics and fine colloids that resulted in high internal fouling. Under the given operating conditions, addition of 1.67 g l −1 PAC appears to be the optimum quantity in terms of cost, flux and soluble COD removal.

Comparative evaluation of the microbial community in biological processes treating industrial and domestic wastewaters

Comparison of the microbial composition and process performance between laboratory scale processes treating domestic and vegetable oil wastewaters. Two laboratory scale modified Ludzack-Ettinger processes were operated under similar operating conditions. One process was fed domestic wastewater and the other an industrial wastewater, vegetable oil effluent. Nitrogen removal capacities of the processes were similar. The industrial process exhibited a lower COD removal capacity and oxygen utilization rate, although a greater mixed liquor volatile suspended solids concentration was observed in the industrial process. Fluorescent in situ hybridization (FISH) with probes EUBmix, ALF1b, BET42a, GAM42a and HGC69a revealed that 81% and 72% of total cells stained with 4', 6-diamidino-2-phenylindole (DAPI) within the domestic and industrial processes respectively bound to EUBmix. This indicated a slightly lower Eubacterial population within the industrial process. The alpha-proteobacteria was the dominant community in the industrial process (31% of EUBmix), while the beta-proteobacteria dominated the domestic process (33% of EUBmix). The findings served to establish a difference in the microbial population between the processes. Therefore, the class alpha-proteobacteria could play a primary role in the degradation of vegetable oil effluent. This research will aid in process design and retrofitting of biological processes treating vegetable oil effluent.

Multi-decadal scale variability in the eastern Baltic cod fishery 1550–1860—Evidence and causes

Identification of periods of high and low cod production, and the reasons for these periods, can increase understanding of variability in populations and ecosystems. In this study we investigate the multi-decadal and multi-century scale variations in the cod population in the eastern Baltic Sea (ICES Subdivisions 25–32). Analytically derived estimates of biomass are available since 1966. These estimates show that biomass increased in the late 1970s–early 1980s, but decreased nearly 10-fold until the early 1990s and is still well below the long-term average. Prior to 1966 the biomass of cod is unknown, as is the relative role of fishing, climate variability/regimes, eutrophication and reduction of marine mammal predator populations. We have begun to investigate whether historical fisheries information (landings, effort, distribution) from before the 1880s is available in Baltic archives and museums, and to what extent this information can be used to interpret variations in this population. We have located fisheries data for different parts of the Baltic for different time periods since the 1550s and have interpreted the findings using current process knowledge of oceanographic mechanisms affecting cod reproduction and ecology in the Baltic Sea. The recovered data show that the Baltic ecosystem was able to support modest-large cod populations even though it was oligotrophic and contained large populations of cod predators (e.g., marine mammals). Current ecosystem management policy in the Baltic as developed and implemented by organisations such as the International Council for the Exploration of the Sea (ICES), the Baltic Marine Environment Protection Commission (HELCOM), the nine coastal countries and the European Union includes recovery of the cod population, a reduction in nutrient loading and measures to promote recovery of seal and harbour porpoise populations. If these policies are successful, the role of predatory fish in the future Baltic could again be substantial and comparable to that which we show existed 450 years ago. However, such a scenario will also require a major reduction in cod fishing mortality and suitable hydrographic conditions which promote successful cod reproduction. Historical ecology investigations in the Baltic can contribute to scientifically based fishery and ecosystem management and recovery plans.