Nitrogen transformations under different conditions in open ponds by means of microalgae-bacteria consortium treating pig slurry

Four open ponds inoculated with microalgae-bacteria consortium treating different swine slurries (fresh and anaerobically digested) were evaluated in terms of nitrogen transformation under optimal and real conditions of temperature and illumination. Ammonium complete depletion was not achieved. Ponds operated under real conditions presented lower ammonium removal. Elimination capacities were around 26 mg N/L d and were subsequently increased with increasing inlet ammonium loading rate. Different nitrogen transformation was observed depending on substrate source. When anaerobically digested slurry was fed to the ponds, nitrification followed by biomass uptake and denitrification were the main nitrogen transformation taking place depending on inlet ammonium loading rate and operational conditions. Ponds fed with fresh slurry exhibited denitrification as the main nitrogen removal mechanism for the pond operated under real conditions while under optimal conditions stripping, denitrification and biomass uptake contributed similarly. Therefore, this study confirmed that the so-claimed nitrogen recovery by microalgae biomass is frequently overestimated.     

A pilot-scale study of total volatile fatty acids production by anaerobic fermentation of sewage in fixed-bed and suspended biomass reactors

A comparative study of a fermentation process for total volatile fatty acids (TVFA) production using pilot-scale fixed-bed (FAS) and suspended biomass (FER) reactors in which similar operational conditions was carried out. The influence of the changes of ambient temperatures at fixed operational conditions was also studied. Oxidation–reduction potential (ORP) increased and effluent pH decreased as the hydraulic retention time (HRT) decreased, which was favourable for TVFA production. Equations describing the ORP and pH variations with the HRT were obtained. ORP variation with HRT for FAS and FER reactors followed a logarithmic function with a regression coefficient, R², equal to 0.98. The variations of pH with HRT followed polynomial functions with regression coefficients of 0.96 and 0.98 for FAS and FER reactors, respectively. Hydrolysis process increased with the experiment duration. At the beginning of the experiment, effluent soluble COD (SCOD) decreased with respect to the influent but further effluent SCOD increased showing higher values compared to the influent. Cold temperatures were more favourable than summer temperatures for the accumulation of TVFA at the liquid effluent. The FAS reactor was more effective in the production of TVFA than the FER reactor. The maximum yields of TVFA were obtained at an organic volumetric loading rate (B_V) of 1.9 g COD/l per day, corresponding to an HRT of 3.4 h, for both reactors. A maximum increase of ammonia and phosphorus was observed at the maximum value of HRT coinciding with an increase of pH and a decrease of ORP, as could be previously observed. The average P/SCOD ratio for the influent and effluent were 0.06 and 0.05, respectively, for FAS and FER reactors. The average Ammonia/SCOD ratio for the influent and effluent were 0.15 and 0.14, respectively. These results demonstrate that effluent quality was improved by the treatment employed in case a further process of nutrient removal is carried out.     

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.     

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.     

An evaluation of single- and separated-phase anaerobic industrial wastewater treatment in fluidized bed reactors

Four fluidized bed reactors were used to evaluate single-and separated-phase anaerobic treatments of a high strength wastewater. Two reactors were fed with a synthetic wastewater, containing glucose as the primary carbon source, with a COD of 1.2 x 10(4) mg/L while the remaining pair were fed with a wastewater with a COD of 6000 mg/L. AT each influent strength, one fluidized bed reactor was operated as a single-phase system while the other was operated as a methanogenic reactor which was preceded by an acidification reactor in a separatedphase system. The reactors were operated under steady-state and variable process conditions. The separated-phase system consistently gave a better quality effluent with lower effluent suspended solids and total COD, and the methane yield was also improved. Under variable process conditions, the separated-phase system was inherently more stable and recovered more rapidly following a shock loading. Propionate and acetate degradation studies indicated that the biomass in the methanogenic fluidized beds of the two-phase systems was more adapted to volatile acid degradation than the biomass in the single-phase fluidized beds.     

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.     

Brewery wastewater treatment using anaerobic inverse fluidized bed reactors

Two anaerobic inverse fluidized bed reactors were utilized to evaluate organic matter removal from brewery wastewater, applying different OLR and testing two support materials. Hydrodynamic tests varying liquid flow and solid concentration were developed on the supports in order to establish operational conditions. A batch colonization stage was applied using 25% active volume of extendosphere and triturated polyethylene as support materials. The reactors were subsequently operated continuously with stepwise increments in organic loading rate until limiting conditions was reached. For the supports studied, IFBR technology was suitable for organic matter removal present in brewery wastewater with COD removal efficiencies greater than 90%. The reactor with triturated polyethylene support showed an excellent COD removal with OLR values up to 10 g COD/Ld, whereas the reactor with extendosphere support had an excellent hydrodynamic and biologic behavior working with OLR values up to 70 g COD/Ld.     

Open and enclosed photobioreactors comparison in terms of organic matter utilization,biomass chemical profile and photosynthetic efficiency

Microalgae systems are currently being researched due to their ability to mitigate carbon dioxide emissions while obtaining a value-added product in the form of biomass. This paper elucidates the ability of microalgal–bacteria consortia for the conversion of organic matter contained in anaerobically digested swine slurry into biomass organic carbon via CO₂ uptake. In this context, the configuration of the reactor, different nitrogen availabilities and different microalgal communities developed in the evaluated reactors (open pond and enclosed tubular photobioreactor) were inferred as a possible reason for the different conversion efficiencies found. The biomass quality in terms of macromolecular cell component obtained under the two different reactors did not show any clear difference. The high efficiency in biomass nitrogen uptake resulted in biomass mainly composed of carbohydrates and proteins. Finally, the photosynthetic efficiency of the two reactor types showed high values which indicated the high efficiency of converting irradiance supplied to the systems into energy stored in biomass.     

Treatment of pig manure liquid digestate in horizontal flow constructed wetlands: Effect of aeration

With the rapid development of scaled anaerobic digestion of pig manure, the generation of liquid anaerobic digestate exceeds the farmland loading capacity, causing serious environmental pollution. Three laboratory‐scale horizontal subsurface flow constructed wetlands (CWs; planted + aeration, planted, and unplanted) were set up to investigate the feasibility of liquid digestate treatment in wetlands. Treatment capacity in different wetlands was evaluated under different influent concentrations (chemical oxygen demand [COD], 5 days biochemical oxygen demand [BOD₅], and nitrogen forms). The effect of aeration and effluent recirculation on organic matter and total nitrogen removal was investigated. Results showed that integrating intermittent aeration in CWs significantly improved the oxygen condition (p < 0.01) in the wetland bed and promoted BOD₅ removal to 90% in aerated CWs as compared with <15% in the unaerated CWs. Meanwhile, COD removal between these three wetlands did not show any difference and varied from 52 to 72% under influent concentration of 200–820 mg/L because of the high content of hard‐degradable organic matter in the liquid digestate. Intermittent aeration resulted in high ammonium removal (>98%) although the influent loading varied from 65 to 350 mg/L. However, intermittent aeration caused nitrate accumulation of 300 mg/L and limited total nitrogen (TN) removal of 33%. To intensify the TN removal, we verified effluent recirculation to increase the removal efficiency of TN to 78%. These results not only show the potential application of CWs for treatment of high‐strength liquid anaerobic digested slurry, but also indicate the significance of intermittent aeration on the enhanced removal of organic matter and ammonium.     

The inhibitory effects and removal of dieldrin in continuous upflow anaerobic sludge blanket reactors

The inhibitory effects and removal efficiency of dieldrin (DLD) in anaerobic reactors were investigated. Anaerobic toxicity assay (ATA) experiments conducted in batch reactors revealed that 30 mg/l DLD had inhibitory effects on the unacclimated mixed anaerobic cultures. Continuous reactor experiments performed in a lab-scale two-stage upflow anaerobic sludge blanket (UASB) reactor system which was fed with ethanol as the sole carbon source, indicated that anaerobic granular cultures could be successfully acclimated to DLD. Chemical oxygen demand (COD) removal efficiencies were 88-92% for the two-stage system. The influent DLD concentration of 10 mg/l was removed by 44-86% and 86-94% in the second stage and overall UASB system, respectively. Biosorption of DLD on granular anaerobic biomass was found to be a significant mechanism for DLD removal in the UASB system. The maximum DLD loading rate and minimum HRT achievable for the first stage UASB reactor were 0.5 mg/lday (76 microg DLD/g VSS.day) and 10 h, respectively, which resulted in the overall COD removal efficiency of 85%.     

rRNA and poly-beta-hydroxybutyrate dynamics in bioreactors subjected to feast and famine cycles

Feast and famine cycles are common in activated sludge wastewater treatment systems, and they select for bacteria that accumulate storage compounds, such as poly-beta-hydroxybutyrate (PHB). Previous studies have shown that variations in influent substrate concentrations force bacteria to accumulate high levels of rRNA compared to the levels in bacteria grown in chemostats. Therefore, it can be hypothesized that bacteria accumulate more rRNA when they are subjected to feast and famine cycles. However, PHB-accumulating bacteria can form biomass (grow) throughout a feast and famine cycle and thus have a lower peak biomass formation rate during the cycle. Consequently, PHB-accumulating bacteria may accumulate less rRNA when they are subjected to feast and famine cycles than bacteria that are not capable of PHB accumulation. These hypotheses were tested with Wautersia eutropha H16 (wild type) and W. eutropha PHB-4 (a mutant not capable of accumulating PHB) grown in chemostat and semibatch reactors. For both strains, the cellular RNA level was higher when the organism was grown in semibatch reactors than when it was grown in chemostats, and the specific biomass formation rates during the feast phase were linearly related to the cellular RNA levels for cultures. Although the two strains exhibited maximum uptake rates when they were grown in semibatch reactors, the wild-type strain responded much more rapidly to the addition of fresh medium than the mutant responded. Furthermore, the chemostat-grown mutant culture was unable to exhibit maximum substrate uptake rates when it was subjected to pulse-wise addition of fresh medium. These data show that the ability to accumulate PHB does not prevent bacteria from accumulating high levels of rRNA when they are subjected to feast and famine cycles. Our results also demonstrate that the ability to accumulate PHB makes the bacteria more responsive to sudden increases in substrate concentrations, which explains their ecological advantage.     

Performance of staged and non-staged up-flow anaerobic sludge bed (USSB and UASB) reactors treating low strength complex wastewater

The use of anaerobic processes to treat low-strength wastewater has been increasing in recent years due to their favourable performance-costs balance. For optimal results, it is necessary to identify reactor configurations that are best suited for this kind of application. This paper reports on the comparative study carried out with two high-rate anaerobic reactor systems with the objective of evaluating their performances when used for the treatment of low-strength, complex wastewater. One of the systems is the commonly used up-flow anaerobic sludge blanket (UASB) reactor. The other is the up-flow staged sludge bed (USSB) system in which the reactor was divided longitudinally into 3, 5 and 7 compartments by the use of baffles. The reactors (9 l) were fed with a synthetic, soluble and colloidal waste (chemical oxygen demand (COD) < 1000 mg/l) and operated at 28°C and 24 h hydraulic retention time. Intermediate flow hydraulics, between plug-flow and completely-mixed, in the UASB and 7 stages USSB reactors allowed efficient degradation of substrates with minimum effluent concentrations. Low number of compartments in the USSB reactors increased the levels of short-circuiting thus reducing substrate removal efficiencies. All reactors showed high COD removal efficiencies (93–98%) and thus can be regarded as suitable for the treatment of low strength, complex wastewater. Staged anaerobic reactors can be a good alternative for this kind of application provided they are fitted with a large enough (≥7) number of compartments to fully take advantage of their strengths. Scale factors seem to have influenced importantly on the comparison between one and multi staged sludge-bed reactors and, therefore, observations made here could change at larger reactor volumes.     

Effect of non-feeding period length on the intermittent operation of UASB reactors treating dairy effluents

Recent environmental concerns have prompted a re-evaluation of conventional management strategies and refueled the search of innovative waste management practices. In this sense, the anaerobic digestion of both fat and the remaining complex organic matter present in dairy wastewaters is attractive, although the continuous operation of high rate anaerobic processes treating this type of wastewaters causes the failure of the process. This work accesses the influence of non-feeding period length on the intermittent operation of mesophilic UASB reactors treating dairy wastewater, in order to allow the biological degradation to catch up with adsorption phenomenon. During the experiments, two UASB reactors were subject to three organic loading rates, ranging from 6 to 12 g(COD) x L(-1) x d(-1), with the same daily load applied to both reactors, each one with a different non-feeding period. Both reactors showed good COD removal efficiencies (87-92%). A material balance for COD in the reactors during the feeding and non-feeding periods showed the importance of the feedless period, which allowed the biomass to degrade substrate that was accumulated during the feeding period. The reactor with the longest non-feeding period had a better performance, which resulted in a higher methane production and adsorption capacity for the same organic load applied with a consequent less accumulation of substrate into the biomass. In addition, both reactors had a stable operation for the organic load of 12 g(COD) x L(-1) x d(-1), which is higher than the maximum applicable load reported in literature for continuous systems (3-6 g(COD) x L(-1) x d(-1)).     

Effects of alternative carbon sources on biological transformation of nitrophenols

The removal of nitrophenols under denitrifying conditions was studied in bench-scale upflow anaerobic sludge blanket (UASB) reactors (R1, R2, R3 and R4) using three different carbon sources. Initially acetate was used as carbon source (substrate) in all the four reactors followed by glucose and methanol. Reactor R1 was kept as control and R2, R3, R4 were fed with 30 mg/l concentration of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP), respectively. Throughout the study the hydraulic retention time (HRT) and COD/NO₃ ^-–N ratio were kept as 24 h and 10, respectively. 2-Aminophenol (2-AP), 4-aminophenol (4-AP) and 2-amino,4-nitrophenol (2-A,4-NP) were found as the major intermediate metabolites of 2-NP, 4-NP and 2,4-DNP degradation, respectively. Methanol was found to be a better carbon source for 4-NP and 2,4-DNP degradation as compared to acetate and glucose, while 2-NP degradation was not influenced much by the change of substrate. Nitrate nitrogen removal was always more than 99%. COD removal efficiency of the nitrophenol fed reactors varied from 85.7% to 97.7%. The oxidation-reduction potential (ORP) inside the reactors dropped, up to –300 mv, with glucose as carbon source. As the reactors were switched over to methanol, ORP increased to –190 mv. The granular sludge developed inside the reactors was light brown in colour when acetate and glucose were used as substrate, which turned dark brown to black at the end of methanol run. Biomass yield in terms of volatile suspended solids was observed as 0.15, 0.089 and 0.14 g per gram of COD removal for acetate, glucose and methanol, respectively.     

Effect of effluent recycling and shock loading on the biodegradation of complex phenolic mixture in hybrid UASB reactors

This study describes the feasibility of anaerobic treatment of synthetic coal wastewater using four identical 13.5L (effective volume) bench scale hybrid up flow anaerobic sludge blanket (HUASB) reactors (R1, R2, R3 and R4) under mesophilic (27+/-5 degrees C) conditions. Synthetic coal wastewater with an average chemical oxygen demand (COD) of 2240 mg/L and phenolics concentration of 752 mg/L was used as substrate. Effluent recirculation was employed at four different effluent to feed recirculation ratios (R/F) of 0.5, 1.0, 1.5 and 2.0 for 100 days to study the effect of recirculation on the performance of the reactors. Phenolics and COD removal was found to improve with increase in effluent recirculation. An effluent to feed recycle ratio of 1.0 resulted in maximum removal of phenolics and COD. Phenolics and COD removal improved from 88% and 92% to 95% each, respectively. The concentration of volatile fatty acids in the effluent was lower than the influent when effluent to feed recirculation was employed. Effect of shock loading on the reactors revealed that phenolics shock load up to 2.5 times increase in the normal input phenolics concentration in the form of continuous shock load for 4days did not affect the reactors performance irreversibly.     

rRNA and Poly-β-Hydroxybutyrate Dynamics in Bioreactors Subjected to Feast and Famine Cycles

Feast and famine cycles are common in activated sludge wastewater treatment systems, and they select for bacteria that accumulate storage compounds, such as poly-β-hydroxybutyrate (PHB). Previous studies have shown that variations in influent substrate concentrations force bacteria to accumulate high levels of rRNA compared to the levels in bacteria grown in chemostats. Therefore, it can be hypothesized that bacteria accumulate more rRNA when they are subjected to feast and famine cycles. However, PHB-accumulating bacteria can form biomass (grow) throughout a feast and famine cycle and thus have a lower peak biomass formation rate during the cycle. Consequently, PHB-accumulating bacteria may accumulate less rRNA when they are subjected to feast and famine cycles than bacteria that are not capable of PHB accumulation. These hypotheses were tested with Wautersia eutropha H16 (wild type) and W. eutropha PHB-4 (a mutant not capable of accumulating PHB) grown in chemostat and semibatch reactors. For both strains, the cellular RNA level was higher when the organism was grown in semibatch reactors than when it was grown in chemostats, and the specific biomass formation rates during the feast phase were linearly related to the cellular RNA levels for cultures. Although the two strains exhibited maximum uptake rates when they were grown in semibatch reactors, the wild-type strain responded much more rapidly to the addition of fresh medium than the mutant responded. Furthermore, the chemostat-grown mutant culture was unable to exhibit maximum substrate uptake rates when it was subjected to pulse-wise addition of fresh medium. These data show that the ability to accumulate PHB does not prevent bacteria from accumulating high levels of rRNA when they are subjected to feast and famine cycles. Our results also demonstrate that the ability to accumulate PHB makes the bacteria more responsive to sudden increases in substrate concentrations, which explains their ecological advantage.     

NOB suppression and adaptation strategies in the partial nitrification–Anammox process for a poultry manure anaerobic digester

Poultry manure contains high levels of ammonia, which result in a suboptimal bioconversion to methane in anaerobic digesters (AD). A simultaneous process of nitrification, Anammox and denitrification (SNAD) in a continuous granular bubble column reactor to treat the anaerobically digested poultry manure was implemented. Thus, two strategies to achieve high efficiencies were proposed in this study: (1) ammonia overload to suppress nitrite oxidizing bacteria (NOB) and (2) gradual adaptation of the partial nitrification–Anammox (PN–A) biomass to organic matter. During the NOB-suppression stage, microbial and physical biomass characterizations were performed and the NOB abundance decreased from 31.3% to 3.3%. During the adaptation stage, with a nitrogen loading rate of 0.34 g L⁻¹ d⁻¹, a hydraulic retention time of 1.24 d and an influent COD/N ratio of 2.63 ± 0.02, a maximum ammonia and total nitrogen removal of 100% and 91.68% were achieved, respectively. The relative abundances of the aerobic and the anaerobic ammonia-oxidizing bacteria were greater than 35% and 40% respectively, during the study. These strategies provided useful design tools for the efficient removal of nitrogen species in the presence of organic matter.     

Effect of COD to sulphate ratio and temperature in expanded-granular-sludge-blanket reactors for sulphate reduction

In an ethanol-fed expanded-granular-sludge-blanket (EGSB) reactor at 33°C, 80–90% of the sulphate load was removed at a rate of 4 g S/l d, provided that at least 6 g chemical oxygen demand (COD) per g sulphate-sulphur was supplied. The reactor started up in a matter of days. Gradually decreasing the ethanol to sulphate ratio (R) to about stoichiometry, resulted in 60–70% sulphate removal at rates of 7 g S/l d. Similar tendencies were observed with ethylene glycol as sole carbon and energy source. Total COD removal never reached more than 70–75%. This was related to a rather high biomass washout. The sulphate removal efficiency decrease when R was set at levels below 6, apparently because sulphate reducing bacteria (SRB) could not compete with methane producing bacteria (MPB) for acetate produced from the substrate dosed. Thermophilic operation at 55°C, after a stepwise increase in the reactor temperature over a period of 23 days, did not favour acetotrophic sulphate reduction. Yet, operation at 48°C and subsequently returning the temperature to 33°C clearly enhanced acetate conversion by SRB. In the case of an electron donor price of 0.035–0.075 USD/kg COD, the cost for operation at R=6 was found to be competitive to that at stoichiometry, i.e. R=2, provided the biogas produced was effectively used.     

Performance of a hybrid anaerobic reactor,combining a sludge blanket and a filter,treating slaughterhouse wastewater

A column reactor, in which the bottom two-thirds were occupied by a sludge blanket and the upper one-third by submerged clay rings, was evaluated using slaughterhouse wastewater as substrate. The reactor was operated at 35°C at loading rates varying from 5 g to 45 g chemical oxygen demand (COD) 1^–1 × day^–1 at an influent concentration of 2450 mg COD 1^–1. A maximum substrate removal rate of 32 g COD 1^–1 × day^–1, coupled with a methane production rate of 6.91 × 1^–1 × day^–1 (STP), was obtained. This removal rate is significantly higher than those previously reported. The rate of substrate utilization by the biomass was 1.22 g COD (g volatile suspended solids)^–1 day^–1. COD removal was over 96% with loading rates up to 25 g COD 1^–1 × day^–1, at higher loading rates performance decreased rapidly. It was found that the filter element of the reactor was highly efficient in retaining biomass, leading to a biomass accumulation yield coefficient of 0.029 g volatile suspended solids g^–1 COD, higher than reported previously for either upflow anaerobic sludge-blanket reactors or anaerobic filters operating independently.     

Anaerobic biodegradation of linear alkylbenzene sulfonate (LAS) in upflow anaerobic sludge blanket (UASB) reactors

The anaerobic biodegradation of Linear Alkylbenzene Sulfonate (LAS) was studied in Upflow Anaerobic Sludge Blanket Reactors (UASB). One reactor was fed with easily degradable substrates and commercial LAS solution during a period of 3 months (Reactor 1), meanwhile a second reactor was fed with a commercial LAS solution without co-substrate (Reactor 2) during 4 months. Both reactors were operated with an organic loading rate of 4–5 mg-LAS/l*day and a hydraulic retention time of one day.The LAS biodegradation was determined by full mass balance. LAS was analysed by HPLC in the liquid phase (influent and effluent streams of the reactors) as well as in the solid phase (granular sludge used as biomass). The results indicate a high level of removal (primary biodegradation: 64–85%). Biodegradation was higher in the absence of external co-substrates than in the presence of additional sources of carbon. This indicates that the surfactant can be partially used as carbon and energy source by anaerobic bacteria. Under the operating conditions used, inhibition of the methanogenic activity or any other negative effects on the biomass due to the presence of LAS were not observed. The methanogenic activity remained high and stable throughout the experiment.