Treatment of low strength soluble wastewaters in UASB reactors

Low strength wastewaters can be those with chemical oxygen demand (COD) below 2,000 mg/l. The anaerobic treatment of such wastewaters has not been fully explored so far. The suboptimal reaction rates with low substrate concentrations, and the presence of dissolved oxygen in the influent are regarded as possible constraints. In this study, the treatment of low strength soluble wastewaters containing ethanol or whey was studied in lab-scale upflow anaerobic sludged bed (UASB) reactors at 30°C. The high treatment performance obtained demonstrates that UASB reactors are viable for treating both types of wastewaters at low COD concentrations. The treatment of the ethanol containing wastewater resulted in COD removal efficiencies exceeding 95% at organic loading rates (OLR) between 0.3 to 6.8 g COD/l-d with influent concentrations in the range of 422 to 943 mg COD/l. In the case of the more complex whey containing wastewater, COD removal efficiencies exceeded 86% at OLRs up to 3.9 g COD/l·, as long as the COD influent was above 630 mg/l. Lowering the COD influent resulted in decreased efficiency with sharper decrease at values below 200 mg/l. Acidification instead of methanogenesis was found to be the rate limiting step in the COD removal at low concentrations, which was not the case when treating ethanol. The effect of dissolved oxygen in the influent as a potential danger in anaerobic treatment was investigated in reactors fed with and without dissolved oxygen. Compared with the control reactor, the reactor receiving oxygen showed no detrimental effects in the treatment performance. Thus, the presence of dissolved oxygen in dilute wastewaters is expected to be of minor importance in practice.     

Identification of bacteria coexisting with anammox bacteria in an upflow column type reactor

Anammox process has attracted considerable attention in the recent years as an alternative to conventional nitrogen removal technologies. In this study, a column type reactor using a novel net type acrylic fiber (Biofix) support material was used for anammox treatment. The Biofix reactor was operated at a temperature of 25°C (peak summer temperature, 31.5°C). During more than 340 days of operation for synthetic wastewater treatment, the nitrogen loading rates of the reactor were increased to 3.6 kg-N/m³/d with TN removal efficiencies reaching 81.3%. When the reactor was used for raw anaerobic sludge digester liquor treatment, an average TN removal efficiency of 72% was obtained with highest removal efficiency of 81.6% at a nitrogen loading rate of 2.2 kg-N/m³/d. Results of extracellular polymeric substances (EPS) quantification revealed that protein was the most abundant component in the granular sludge and was found to be almost twice than that in the sludge attached to the biomass carriers. The anammox granules in the Biofix reactor illustrated a dense morphology substantiated by scanning electron microscopy and EPS results. The results of DNA analyses indicated that the anammox strain KSU-1 might prefer relatively low nutrient levels, while the anammox strain KU2 strain might be better suited at high nutrient concentration. Other types of bacteria were also identified with the potential of consuming dissolved oxygen in the influent and facilitating survival of anammox bacteria under aerobic conditions.     

Start-up and operation of anaerobic biofilters with packing alternatives

Four types of anaerobic upflow biofilters: non-packed (NP-AUBF), two-stage (2S-AUBF), multi-stage (MS-AUBF) and fully-packed (FP-AUBF), were tested for their start-up and operational performance characteristics. The volume of each filter was 12.1 dm³ (10 cm I.D.x155 cm in height).Stepwise seeding was conducted and the effect on the reduction of COD and gas production was monitored. When each reactor was loaded with 2 and 4 kg COD/m³-day of synthetic waste simulating alcohol production plant, 2S-, MS-, FP-AUBF had treatment efficiencies of 89–93%, while NP-AUBF showed efficiencies lower than 50%. As a conclusion, 2S- or MS-AUBF can be used as efficiently as FP-AUBF, while the amount of packings in the former is half that in FP-AUBF.     

Nitrogen removal via simultaneous partial nitrification,anammox and denitrification (SNAD) process under high DO condition

The simultaneous partial nitrification, anammox and denitrification (SNAD) process for treating domestic wastewater was investigated in a sequencing batch reactor (SBR). The SBR was operated with air flow rate of 500 L h^?1 at 30 °C. Domestic wastewater was used as influent and Kaldnes rings were used as biomass carriers. In the beginning, long aeration condition was implemented to cultivate nitrification biofilm. Afterwards, intermittent aerobic condition was conducted during the cycle operation. The influent organic matter loading rate was improved by reducing the aeration and mixing times. Consequently, when the SNAD biofilm reactor was fed with the organic matter loading rate of 0.77 (kg COD m^?3 d^?1), the bio-bubbles appeared in the reactor and the total inorganic nitrogen (TIN) removal efficiency decreased. After the organic matter loading rate decreased to 0.67 (kg COD m^?3 d^?1), the reactor showed excellent nitrogen removal performance. The TIN removal efficiency varied between 80 and 90 %, and the average TIN removal loading rate was 0.22 (kg TIN m^?3 d^?1). Additionally, the scanning electron microscope (SEM) observation confirmed that the anammox bacteria located in the inner part of the carriers. Finally, the microbial community analysis of 16S rRNA gene cloning revealed that the anammox bacteria on the carriers consisted of three main genuses: Candidatus Brocadia sp., Candidatus Brocadia caroliniensis and Candidatus Brocadia fulgida.     

Treatment of phenolic wastes in an aerated submerged fixed-film (ASFF) bioreactor

The biological removal of phenol was studied in a multi-stage fixed-film reactor at phenol concentrations in the range of 190–900 mg l⁻¹, hydraulic loadings of 0.02–0.22 m³ m⁻² day⁻¹ and temperatures of 20–35°C. Phenol removals up to 99.9% were obtained at 20°C but the efficiency decreased as the loading rate or phenol concentration was increased. The reactor coped with organic overloads better than with hydraulic overloads. Removal efficiencies increased as temperature was increased. Reactor performance was stable under extreme loadings and the reactor was capable of handling a ten-fold increase in loading with less than 20% loss in phenol removal efficiency. A large amount of attached biomass was retained in the reactor and was mostly present in the first stage where the majority of organic removal occurred.     

Aerobic granulation and nitrogen removal with the effluent of internal circulation reactor in start-up of a pilot-scale sequencing batch reactor

Aerobic granular sludge was successfully cultivated with the effluent of internal circulation (IC) reactor in a pilot-scale sequencing batch reactor (SBR) using activated sludge as seeding sludge. N removal was investigated in the start-up of aerobic granulation process. Initially, the phenomenon of partial nitrification was observed and nitrite accumulation rates (NO₂ ^?-N/NO _x ^? -N) were between 84.6 and 99.1?%. It was potentially caused by ammonium oxidizing bacteria (AOB) in the seeding activated sludge, high external environmental temperature (~32?°C) and free ammonia (FA) concentration. After 50?days’ running, the aerobic granules-based bioreactor demonstrated perfect performance in simultaneous removal of organic matter and ammonia nitrogen, and average removal efficiencies were maintained above 93 and 96?%, respectively. The maximum nitrogen removal efficiency of 83.1?% was achieved after the formation of aerobic granules. The average diameter of mature aerobic granular sludge mostly ranged from 0.5 to 1.0?mm. Furthermore, one typical cyclic test indicated that pH and DO profiles could be used as effective parameters for biological reactions occurring in the aerobic/anoxic process. The obtained results could provide further information on the cultivation of aerobic granular sludge with practical wastewater, especially with regard to nitrogen-rich industrial wastewater.     

Effects of nitrobenzene concentration and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor (ABR)/continuously stirred tank reactor (CSTR) system

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention times (HRT) on the treatment of NB were investigated in a sequential anaerobic baffled reactor (ABR)/aerobic completely stirred tank reactor (CSTR) system. In the first step of the study, the maximum COD removal efficiencies were found as 88% and 92% at NB concentrations varying between 30 mg L^?1 and 210 mg L^?1 in ABR. The minimum COD removal efficiency was 79% at a NB concentration of 700 mg L^?1. The removal efficiency of NB was nearly 100% for all NB concentrations in the ABR reactor. The methane gas production and the methane gas percentage remained stable (1500 mL day^?1 and 48–50%, respectively) as the NB concentration was increased from 30 to 210 mg L^?1. In the second step of the study it was found that as the HRT decreased from 10.38 days to 2.5 days the COD removal efficiencies decreased slightly from 94% to 92% in the ABR. For maximum COD and NB removal efficiencies the optimum HRT was found as 2.5 days in the ABR. The total COD removal efficiency was 95% in sequential anaerobic (ABR)/aerobic (CSTR) reactor system at a minimum HRT of 1 day. When the HRT was decreased from 10.38 days to 1 day, the methane percentage decreased from 42% to 29% in an ABR reactor treating 100 mg L^?1 NB. Nitrobenzene was reduced to aniline under anaerobic conditions while aniline was mineralized to catechol with meta cleavage under aerobic conditions.     

Evaluation of an on-site pilot static granular bed reactor (SGBR) for the treatment of slaughterhouse wastewater

An on-site pilot-scale static granular bed reactor (SGBR) system was evaluated for treating wastewater from a slaughterhouse in Iowa. The study evaluated SGBR reactor suitability for slaughterhose wastewater having high particulate COD concentration (7.9 ± 4.3 g COD/L) at 0.3–1.4 m³/m²/day of the surface loading rates. High organic removal efficiency (over 95% of TSS and VSS removal) was obtained due to the consistent treatability of SGBR system during operation at HRTs of 48, 36, 30, 24, and 20 h. The average effluent TSS, VSS, COD, soluble COD, and BOD₅ concentrations were 84, 71, 301,197, and 87 mg/L, respectively. An effective backwash procedure was performed once every 7–14 days to waste a portion of the accumulated solids in the system. This procedure limited the increase in hydraulic head loss and maintained the system stability. COD removal efficiencies greater than 95% were achieved at organic loading rates ranging from 0.77 to 12.76 kg/m³/day.     

A half-submerged integrated two-phase anaerobic reactor for agricultural solid waste codigestion

Anaerobic digestion is widely used in bioenergy recovery from waste. In this study, a half-submerged, integrated, two-phase anaerobic reactor consisting of a top roller acting as an acidogenic unit and a recycling bottom reactor acting as a methanogenic unit was developed for the codigestion of wheat straw (WS) and fruit/vegetable waste (FVW). The reactor was operated for 21 batches (nearly 300 d). Anaerobic granular sludge was inoculated into the methanogenic unit. The residence time for the mixed waste was maintained as 10 d when the operation stabilized, and the temperature was kept at 35 °C. The highest organic loading rate was 1.37 kg VS/(m³ d), and the maximum daily biogas production was 328 L/d. Volatile solid removal efficiencies exceeded 85%. WS digestion could be confirmed, and efficiency was affected by both the ratio of WS to FVW and the loading rate. The dominant bacteria were Bacteroides-like species, which are involved in glycan and cellulose decomposition. Methanogenic community structures, pH levels, and volatile fatty acid concentrations in the acidogenic and methanogenic units differed, indicating successful phase separation. This novel reactor can improve the mass transfer and microbial cooperation between acidogenic and methanogenic units and can efficiently and steady codigest solid waste.     

Comparison of startup and anaerobic wastewater treatment in UASB, hybrid and baffled reactor

An experimental study was carried out to compare the performance of selected anaerobic high rate reactors operated simultaneously at 37?°C. The three reactors, namely upflow anaerobic sludge bed reactor (UASB), hybrid of UASB reactor and anaerobic filter (anaerobic hybrid reactor – AHR) and anaerobic baffled reactor (ABR), were inoculated with the anaerobic digested sludge from municipal wastewater treatment plant and tested with synthetic wastewater. This wastewater contained sodium acetate and glucose with balanced nutrients and trace elements (COD 6000?mg?·?l^?1). Organic loading rate (B _v ) was increased gradually from an initial 0.5?kg?·?m^?3?·?d^?1 to 15?kg?·?m^?3?·?d^?1 in all the reactors. From the comparison of the reactors' performance, the lowest biomass wash-out resulted from ABR. In the UASB, significant biomass wash-out was observed at the B _v 6?kg?·?m^?3?·?d^?1, and in the AHR at the B _v 12?kg?·?m^?3?·?d^?1. The demand of sodium bicarbonate for pH maintenance in ABR was two times higher as for UASB and AHR. The efficiency of COD removal was comparable for all three reactors – 80–90%. A faster biomass granulation was observed in the ABR than in the other two reactors. This fact is explained by the kinetic selection of filamentous bacteria of the Methanotrix sp. under a high (over 1.5?g?·?l^?1) acetate concentration.     

Bioreactor microbial ecosystems for thiocyanate and cyanide degradation unravelled with genome‐resolved metagenomics

Gold ore processing uses cyanide (CN^?), which often results in large volumes of thiocyanate‐ (SCN^?) contaminated wastewater requiring treatment. Microbial communities can degrade SCN^? and CN^?, but little is known about their membership and metabolic potential. Microbial‐based remediation strategies will benefit from an ecological understanding of organisms involved in the breakdown of SCN^? and CN^? into sulfur, carbon and nitrogen compounds. We performed metagenomic analysis of samples from two laboratory‐scale bioreactors used to study SCN^? and CN^? degradation. Community analysis revealed the dominance of Thiobacillus spp., whose genomes harbour a previously unreported operon for SCN^? degradation. Genome‐based metabolic predictions suggest that a large portion of each bioreactor community is autotrophic, relying not on molasses in reactor feed but using energy gained from oxidation of sulfur compounds produced during SCN^? degradation. Heterotrophs, including a bacterium from a previously uncharacterized phylum, compose a smaller portion of the reactor community. Predation by phage and eukaryotes is predicted to affect community dynamics. Genes for ammonium oxidation and denitrification were detected, indicating the potential for nitrogen removal, as required for complete remediation of wastewater. These findings suggest optimization strategies for reactor design, such as improved aerobic/anaerobic partitioning and elimination of organic carbon from reactor feed.     

Urine nitrification with a synthetic microbial community

During long-term extra-terrestrial missions, food is limited and waste is generated. By recycling valuable nutrients from this waste via regenerative life support systems, food can be produced in space. Astronauts’ urine can, for instance, be nitrified by micro-organisms into a liquid nitrate fertilizer for plant growth in space. Due to stringent conditions in space, microbial communities need to be be defined (gnotobiotic); therefore, synthetic rather than mixed microbial communities are preferred. For urine nitrification, synthetic communities face challenges, such as from salinity, ureolysis, and organics.In this study, a synthetic microbial community containing an AOB (Nitrosomonas europaea), NOB (Nitrobacter winogradskyi), and three ureolytic heterotrophs (Pseudomonas fluorescens, Acidovorax delafieldii, and Delftia acidovorans) was compiled and evaluated for these challenges. In reactor 1, salt adaptation of the ammonium-fed AOB and NOB co-culture was possible up to 45 mS cm⁻¹, which resembled undiluted nitrified urine, while maintaining a 44 ± 10 mg NH₄⁺–N L⁻¹ d⁻¹ removal rate. In reactor 2, the nitrifiers and ureolytic heterotrophs were fed with urine and achieved a 15 ± 6 mg NO₃⁻–N L⁻¹ d⁻¹ production rate for 1% and 10% synthetic and fresh real urine, respectively. Batch activity tests with this community using fresh real urine even reached 29 ± 3 mg N L⁻¹ d⁻¹. Organics removal in the reactor (69 ± 15%) should be optimized to generate a nitrate fertilizer for future space applications.     

Effect of reactor height on mixing characteristics and performance of the anaerobic downflow stationary fixed-film (DSFF) reactor

Three anaerobic downflow stationary fixed-film (DSFF) reactors using multiple vertical clay channels of different heights (31, 92 and 183 cm) and treating bean blanching waste showed improved performance and mixing characteristics with increased reactor height. A start-up period of 100 days was necessary to achieve the best performance in terms of loading rate (up to 9.5 kg Chemical Oxygen Demand (COD) m^?3 d^?1) and methane production rate (up to 2.7 m³ m^?3 d^?1). During this period, differences in performance could only be related to the surface-to-volume ratio. At steady-state, mixing analysis indicated that the reactors deviated from the perfect-mixed pattern. Some dead space and shortcircuiting occurred. The amount of dead space due to biomass accumulation decreased as the reactor height increased (up to 44% for the shortest reactor). The COD removal efficiency was dependent on loading rate, decreasing from 90% at a loading rate of 1.0 kg COD m^?3 d^?1 to 75% at 7.0 kg COD m^?3 d^?1. However, the effect was more pronounced in the shortest reactor than in the tallest one. The improvement in mixing characteristics in the tallest reactor could be related to the higher liquid velocity inside channels which in turn permitted better support utilization and concomitant better COD removal. Data also suggest that it may be preferable to scale-up vertically rather than horizontally in order to maximize the liquid velocity in the channels.     

Biological treatment of oilfield-produced water: A field pilot study

A field test was conducted on a hydrolysis acidification/bio-contact oxidation system (HA/BCO) to treat oilfield-produced water with high salinity. By operating the biodegradation system for three months with a hydraulic retention time (HRT) of 32 h and a volumetric load of 0.28 kg COD m³ d^?1, the treatment process achieved mean removal efficiencies of 63.5% for chemical oxygen demand (COD), 45% for NH₃-N, 79.5% for total suspended solid (TSS), and 68.0% for total petroleum hydrocarbon (TPH). GC/MS was used to analyze relative changes of components of main organic waste in a process indicating that the influent wastewater contained organic compounds from C₁₂H₂₆ to C₃₅H₇₂, which could be degraded effectively with the coordinated action of hydrolysis acidification and aerobic treatment. The use of maize powder can enhance environmental adaptability of microorganisms and biodegradation ability and is recommended as a nutrient supplement to maintain good treatment performance.     

Biodegradation of dimethyl phthalate with high removal rates in a packed-bed reactor

Biological treatment of a dimethyl phthalate (DMP)-containing waste stream was evaluated in packed-bed bioreactors using an acclimated mixed bacterial culture. The passive immobilization start-up strategy was successful in the development of a stable biofilm on the packing material in the reactor. Nutrient supplementation significantly improved the removal efficiency. High removal rates with 100% efficiencies of DMP removal were achieved up to the phthalate-loading rate of 560 g/m³ h.     

Leachate treatment and greenhouse gas emission in subsurface horizontal flow constructed wetland

Organic and nitrogen removal efficiencies in subsurface horizontal flow wetland system (HSF) with cattail (Typha augustifolia) treating young and partially stabilized solid waste leachate were investigated. Hydraulic loading rate (HLR) in the system was varied at 0.01, 0.028 and 0.056 m³/m² d which is equivalent to hydraulic retention time (HRT) of 28, 10 and 5 d. Average BOD removals in the system were 98% and 71% when applied to young and partially stabilized leachate at HLR of 0.01 m³/m² d. In term of total kjeldahl nitrogen, average removal efficiencies were 43% and 46%. High nitrogen in the stabilized leachate adversely affected the treatment performance and vegetation in the system. Nitrogen transforming bacteria were found varied along the treatment pathway. Methane emission rate was found to be highest at the inlet zone during young leachate treatment at 79–712 mg/m² d whereas CO₂ emission ranged from 26–3266 mg/m² d. The emission of N₂O was not detected.     

Use of the upflow sludge blanket (USB) reactor concept for biological wastewater treatment,especially for anaerobic treatment

In recent years considerable effort has been made in the Netherlands toward the development of a more sophisticated anaerobic treatment process, suitable for treating low a strength wastes and for applications at liquid detention times of 3–4 hr. The efforts have resulted in new type of upflow anaerobic sludge blanket (UASB) process, which in recent 6 m³ pilot-plant experiments has shown to be capable of handling organic space loads of 15–40 kg chemical oxygen demand (COD)·m^?3/day at 3–8 hr liquid detention times. In the first 200 m³ full-scale plant of the UASB concept, organic space loadings of up to 16 kg COD·m^?3/day could be treated satisfactorily at a detention times of 4 hr, using sugar beet waste as feed. The main results obtained with the process in the laboratory as well as in 6 m³ pilot plant and 200 m³ full-scale experiments are presented and evaluated in this paper. Special attention is given to the main operating characteristics of the UASB reactor concept. Moreover, some preliminary results are presented of laboratory experiments concerning the use of the USB reactor concept for denitrification as well as for the acid formation step in anaerobic treatment. For both purposes the process looks feasible because very satisfactory results with respect to denitrification and acid formation can be achieved at very high hydraulic loads (12 day^?1) and high organic loading rates, i.e., 20 kg COD·m^?3/day in the denitrification and 60–80 kg COD·m^?3/day in the acid formation experiments.     

Anaerobic treatment of low-strength wastewater with a high fraction of particulate matter in an unconventional two-phase ASBRs system

The results of a two-phase anaerobic system using anaerobic sequencing batch reactors (ASBRs), treating low-strength wastewater (COD ∼ 500 mg/L) with a high fraction of particulate organic matter (70%, COD basis), are presented. Two reactors in series were used; the first one was hydrolytic–acidogenic, while the second one was methanogenic. This configuration was proposed to promote high efficiency solids removal. During the experiment, 69% and 50% efficiencies of total COD removal were obtained for OLRs of 0.63 and 1.22 kgCOD/(m³ d), respectively. Values of the solubilized organic fraction (SOF) achieved in the hydrolytic–acidogenic reactor were within the range of 0.3–0.6 gCOD_solubilized/gpCOD_removed, and the average acidified organic fraction (AOF) was 0.6 gCOD_VFA-produced/gsCOD_fed. The methanogenic reactor had a VFA removal fraction (VFARF) between 0.4 and 0.6 gCOD_VFA-removed/gCOD_VFA-fed for the OLR of 0.63 and 1.22. The two-phase ASBR system is suitable, and can be implemented, for the anaerobic treatment of this kind of wastewater.     

Anammox for ammonia removal from pig manure effluents: Effect of organic matter content on process performance

The anammox process, under different organic loading rates (COD), was evaluated using a semi-continuous UASB reactor at 37 °C. Three different substrates were used: initially, synthetic wastewater, and later, two different pig manure effluents (after UASB-post-digestion and after partial oxidation) diluted with synthetic wastewater. High ammonium removal was achieved, up to 92.1 ± 4.9% for diluted UASB-post-digested effluent (95 mg COD L^?1) and up to 98.5 ± 0.8% for diluted partially oxidized effluent (121 mg COD L^?1). Mass balance clearly showed that an increase in organic loading (from 95 mg COD L^?1 to 237 mg COD L^?1 and from 121 mg COD L^?1 to 290 mg COD L^?1 for the UASB-post-digested effluent and the partially oxidized effluent, respectively) negatively affected the anammox process and facilitated heterotrophic denitrification. Partial oxidation as a pre-treatment method improved ammonium removal at high organic matter concentration. Up to threshold organic load concentration of 142 mg COD L^?1 of UASB-post-digested effluent and 242 mg COD L^?1 of partially oxidized effluent, no effect of organic loading on ammonia removal was registered (ammonium removal was above 80%). However, COD concentrations above 237 mg L^?1 (loading rate of 112 mg COD L^?1 day^?1) for post-digested effluent and above 290 mg L^?1 (loading rate of 136 mg COD L^?1 day^?1) for partially oxidized effluent resulted in complete cease of ammonium removal. Results obtained showed that, denitrification and anammox process were simultaneously occurring in the reactor. Denitrification became the dominant ammonium removal process when the COD loading was increased.     

Nitrification, denitrification, and dechlorination in bleached kraft pulp mill wastewater

This study deals with combining the biologi cal removal of organic halogens with the removal of nitrogen from bleached kraft pulp mill wastewater in fluidized-bed reactors under nitrifying and denitrifying conditions. Untreated and biotreated bleached kraft pulp mill wastewaters had no detrimental effect on nitrification or denitrification. The nitrifying biofilm reactor, pregrown on synthetic inorganic feed with ammonia, removed without a lag phase adsorbable organic halogens [7.2 mg Cl (g biomass volatile solids)⁻¹day⁻¹] from bleached kraft pulp mill wastewater and selected chlorophenols from synthetic wastewater. Electron microscopical examination of the biofilm showed that bacteria, morphologically similar to the nitrifying species Nitrosomonas or Nitrobacter, and Nitrosospira were dominant. The denitrifying fluidized-bed reactor, pregrown on nitrate and methanol, denitrified without a lag phase bleached kraft pulp mill wastewater. Under denitrifying conditions, 35% of the total organic carbon content of untreated bleached kraft pulp mill waste water was removed. The reducing power delivered by untreated bleached kraft pulp mill wastewater for denitrification was 2 mmol electrons/mmol carbon mineralized. Dechlorination under denitrifying conditions was negligible. Received: 21 November 1996 / Received revision: 27 January 1997 / Accepted: 1 February 1997