Grey water treatment in upflow anaerobic sludge blanket (UASB) reactor at different temperatures

The treatment of grey water in two upflow anaerobic sludge blanket (UASB) reactors, operated at different hydraulic retention times (HRTs) and temperatures, was investigated. The first reactor (UASB-A) was operated at ambient temperature (14-25 degrees C) and HRT of 20, 12 and 8 h, while the second reactor (UASB-30) was operated at controlled temperature of 30 degrees C and HRT of 16, 10 and 6 h. The two reactors were fed with grey water from 'Flintenbreite' settlement in Luebeck, Germany. When the grey water was treated in the UASB reactor at 30 degrees C, total chemical oxygen demand (CODt) removal of 52-64% was achieved at HRT between 6 and 16 h, while at lower temperature lower removal (31-41%) was obtained at HRT between 8 and 20 h. Total nitrogen and phosphorous removal in the UASB reactors were limited (22-36 and 10-24%, respectively) at all operational conditions. The results showed that at increasing temperature or decreasing HRT of the reactors, maximum specific methanogenic activity of the sludge in the reactors improved. As the UASB reactor showed a significantly higher COD removal (31-64%) than the septic tank (11-14%) even at low temperature, it is recommended to use UASB reactor instead of septic tank (the most common system) for grey water pre-treatment. Based on the achieved results and due to high peak flow factor, a HRT between 8 and 12 h can be considered the suitable HRT for the UASB reactor treating grey water at temperature 20-30 degrees C, while a HRT of 12-24 h can be applied at temperature lower than 20 degrees C.     

Factors affecting the activity of anammox bacteria during start up in the continuous culture reactor.

Factors affecting cultivation of extremely slow-growing bacteria (anaerobic ammonium oxidiser, doubling time 11 days) were investigated by using upflow anaerobic sludge blanket (UASB) reactors which can maintain high solid retention time. The effects of concentrations of DO, free ammonia (FA), and nitrite on activation of anammox activity were tested during the start-up period. The reactor was inoculated with granular sludge collected from a full-scale UASB reactor used for treating brewery wastewater, and sludge from a piggery wastewater treatment plant and rotating biological contactor treating sewage. Results of continuous operation showed that concentrations of DO, free ammonia (FA) and nitrite in the reactors played a key role in stimulating the anammox activity during start-up period. It is crucial to keep DO below 0.2 ppm, FA below 2 mg/L and nitrite nitrogen below 35 mg/L to cultivate anammox cells in the continuous bioreactor. When the levels of DO, FA and nitrite in the influent were controlled at less than the inhibition levels, the anammox activity increased gradually in the anaerobic condition. Addition of hydrogen sulphide into the reactor enhanced anammox activity in the continuous culture. Through the SEM, TEM and FISH analysis, anammox bacteria were detected in the granular sludge after 3 months of continuous operation.     

Evaluation of sludge properties in a pilot-scale UASB reactor for sewage treatment in a temperate region

In this study, continuous operation of a pilot-scale upflow anaerobic sludge blanket (UASB) reactor for sewage treatment was conducted for 630 days to investigate the physical and microbial characteristics of the retained sludge. The UASB reactor with a working volume of 20.2 m(3) was operated at ambient temperature (16-29 °C) and seeded with digested sludge. After 180 days of operation, when the sewage temperature had dropped to 20 °C or lower, the removal efficiency of both total suspended solids (TSS) and total biochemical oxygen demand (BOD) deteriorated due to washout of retained sludge. At low temperature, the cellulose concentration of the UASB sludge increased owing to the rate limitation of the hydrolytic reaction of suspended solids in the sewage. However, after an improvement in sludge retention (settleability and concentration) in the UASB reactor, the process performance stabilized and gave sufficient results (68% of TSS removal, 75% of total BOD removal) at an hydraulic retention time (HRT) of 9.7 h. The methanogenic activity of the retained sludge significantly increased after day 246 due to the accumulation of Methanosaeta and Methanobacterium following the improvement in sludge retention in the UASB reactor. Acid-forming bacteria from phylum Bacteroidetes were detected at high frequency; thus, these bacteria may have an important role in suspended solids degradation.     

Stability and activity of anaerobic sludge from UASB reactors treating sewage in subtropical regions.

The production of small amounts of well-stabilized biological sludge is one of the main advantages of upflow anaerobic sludge bed (UASB) reactors over aerobic wastewater treatment systems. In this work, sludge produced in three pilot-scale UASB reactors used to treat sewage under subtropical conditions was assessed for both stability and specific methanogenic activity. Stability of primary sludge from settling tanks and digested sludge from conventional sludge digesters was also measured for comparison purposes. Kinetic parameters like the hydrolysis rate constant and the decay rate constant were calculated. High stability was observed in sludge from UASB reactors. Methanogenic activity in anaerobic sludges was relatively low, probably due to the low organic matter concentration in influent sewage. Knowledge on sludge growth rate, stability, and activity might be very useful to optimize sludge management activities in full-scale UASB reactors.     

Treatment of textile dyes in two-phase and single-phase anaerobic bio-treatment systems.

This research integrates two different concepts of anaerobic biotechnology- two-phase anaerobic treatment and anaerobic granular sludge bed technology, in treatment of colored wastewaters from textile industries. Four anaerobic reactors based on upflow anaerobic sludge blanket (UASB) technology were used as acid reactors and an expanded granular sludge bed (EGSB) reactor was used as a methane reactor. A conventional single-phase anaerobic reactor, working on EGSB technology was run in parallel to compare the performances of the two systems. Reactors were operated at different hydraulic retention times. The results from the study, which span over a period of 400 days, indicated that the two-phase system produces a higher quality of effluent in terms of color, COD and suspended solids than single-phase anaerobic treatment when operated under similar conditions. Alkalinity requirement of two-phase system was also observed to be lower than that of single-phase system which is important regarding design consideration.     

Granulation of Anammox microorganisms in up-flow reactors.

Experimental studies were performed to evaluate the feasibility of granulation of Anammox microorganisms for biomass retention in up-flow reactors. Two experimental studies, one using a 6.4-L lab-scale reactor with synthetic medium and the other using a 200-L pilot-scale reactor with half-nitrified reject water from a sludge digester were conducted. To enhance the granulation process, seed granules from a UASB reactor were added to both experimental reactors. Granulation of Anammox microorganisms was observed using both the synthetic medium and the reject water. The core of a large proportion of Anammox granules retained part of the original seed biomass. The Anammox granules had a slightly lower density than the seed granules from the UASB process, but the size and other physical properties were comparable. The successful granulation of the Anammox microorganisms led to a stable nitrogen removal performance. The maximum nitrogen removal rate of the lab-scale reactor was observed to be 2.9 kg/(m3 x d) after 173 days of operation and that of the pilot-scale reactor was 6.4 kg/(m3 x d) after 12 months of operation.     

UASB reactor for domestic wastewater treatment at low temperatures: a comparison between a classical UASB and hybrid UASB-filter reactor.

The performance of an upflow anaerobic sludge blanket (UASB) reactor and a hybrid UASB-filter reactor was investigated and compared for the treatment of domestic wastewater at different operational temperatures (28, 20, 14 and 10 degrees C) and loading rates. For each temperature studied a constant CODt removal was observed as long as the upflow velocity was lower than 0.35 m/h. At these upflow velocities similar removals were observed for both reactor types at 28 and 20 degrees C, 82 and 72% respectively. However, at 14 and 10 degrees C the UASB reactor showed a better COD removal (70% and 48%, respectively) than the hybrid reactor (60% and 38%). COD removal resulted from biological degradation and solids accumulation in the reactors. At 28 degrees C, a constant 200 g sludge mass was observed in both reactors and COD removal was attributed to biological degradation only. At lower temperatures, solids accumulation was observed in addition to biological degradation with an increase in reactor sludge as the temperature decreased. The decrease in biological degradation at lower temperatures was offset by solids accumulation and explains the similar overall COD removal efficiency observed at 28 degrees C, 20 degrees C and 14 degrees C. The decrease in temperature was also followed by an increase in the effluent TSS concentration in both reactors. At 14 and 10 degrees C a lower effluent TSS concentration and better performance was observed in the UASB reactor.     

Anaerobic bioprocessing of sewage sludge, focusing on degradation of linear alkylbenzene sulfonates (LAS).

Anaerobic degradation of sludge amended with linear alkylbenzene sulfonates (LAS) was tested in a one stage continuous stirred tank reactor (CSTR) and a two stage reactor system consisting of a CSTR as first step and upflow anaerobic sludge bed (UASB) reactor as the second step. Anaerobic removal of LAS was only observed at the second step but not at the first step. Removal of LAS in the UASB reactors was approx. 80% where half was due to absorption and the other half was apparently due to biological removal as shown from the LAS mass balance. At the end of the experiment the reactors were spiked with 14C-LAS which resulted in 5.6% 14CO2 in the produced gas. Total mass balance of the radioactivity was however not achieved. In batch experiments it was found that LAS at concentrations higher than 50 mg/l is inhibitory for most microbial groups of the anaerobic process. Therefore, low initial LAS concentration is a prerequisite for successful LAS degradation. The results from the present study suggest that anaerobic degradation of LAS is possible in UASB reactors when the concentration of LAS is low enough to avoid inhibition of microorganisms active in the anaerobic process.     

Comparing the performance of UASB and GRABBR treating low strength wastewaters

Anaerobic technologies have proved successful in the treatment of various high strength wastewaters with perceptible advantages over aerobic systems. The applicability of anaerobic processes to treat low strength wastewaters has been increasing with the evolution of high-rate reactors capable of achieving high sludge retention time (SRT) when operating at low HRT. However, the performance of these systems can be affected by high variations in flow and wastewater composition. This paper reports on the comparative study carried out with two such high rate reactors systems to evaluate their performances when used for the treatment of low strength wastewaters at high hydraulic rates. One of the two systems is the most commonly used upflow anaerobic sludge blanket (UASB) reactor in which all reactions occur within a single vessel. The other is the granular bed baffled reactor (GRABBR) that encourages different stages of anaerobic digestion in separate vessels longitudinally across the reactor. The reactors, with equal capacity of 10 litres, were subjected to increasing organic loading rates (OLRs) and hydraulic retention times (HRTs) of up to 60 kg COD m(-3) d(-1) and 1 h respectively. Results show that the GRABBR has greater processes stability at relatively low HRTs, whilst the UASB seems to be better equipped to cope with organic overloads or shockloads. The study also shows that the GRABBR enables the harvesting of biogas with greater energetic value and hence greater re-use potential than the UASB. Biogas of up to 86% methane content is obtainable with GRABBR treating low strength wastewaters.     

The effects of hydraulic and organic shock loads on the robustness of upflow anaerobic sludge blanket reactors treating sewage.

In this investigation, the robustness and stability of UASB reactors was evaluated on the basis of four indicators: (i) COD removal efficiency; (ii) effluent variability; (iii) pH stability; and (iv) recovery time. The experiments were carried out using six pilot-scale UASB reactors fed with domestic sewage and operated under different operational conditions. After establishment of a "steady-state", organic and hydraulic shock loads (six times the loading rate during six hours) were imposed. The results show that the UASB reactors are robust systems with regards to COD removal efficiency and pH stability when exposed to shock loads. However, this reactor cannot attenuate the imposed fluctuation in the influent COD. A secondary treatment unit is needed to retain the expelled sludge occurring as a result of a hydraulic shock load, or prior to the shock, a sufficient amount of sludge needs to be discharged from the reactor.     

Importance of the ammonia volatilization rates in shallow maturation ponds treating UASB reactor effluent

This study aimed at determining the influence of ammonia volatilization on nitrogen removal in polishing (maturation) ponds treating sanitary effluent from upflow anaerobic sludge blanket (UASB) reactors in the city of Belo Horizonte, Brazil. An apparatus for the capture and absorption of volatilized ammonia in three polishing ponds in series was installed. Volatilized ammonia was captured by a chamber on the surface of the ponds and dissolved in boric acid solution, in order to estimate the amount of ammonia per unit surface area of each pond. Low rates of volatilization, below 0.2 kg/ha.d, in about 75% of samples from all the ponds, were observed. The mass balance of ammonia nitrogen of the ponds showed that the volatilization represented only about 2% of the total removal of nitrogen from the polishing ponds. The results obtained suggest that ammonia volatilization was a mechanism of little importance in nitrogen removal in the investigated polishing ponds.     

Anaerobic digestion potential for ecological and decentralised sanitation in urban areas.

The potential of anaerobic digestion in ecological and decentralised sanitation has been investigated in this research. Different anaerobic digestion systems were proposed for the treatment of sewage, grey water, black water and faeces. Moreover, mathematical models based on anaerobic digestion model no.1 (ADM1) were developed for determination of a suitable design for each system. For stable performance of an upflow anaerobic sludge blanket (UASB) reactor treating sewage, the model results indicated that optimisation of wastewater conversion to biogas (not COD removal) should be selected for determination of the hydraulic retention time (HRT) of the reactor. For the treatment of sewage or black water in a UASB septic-tank, the model results showed that the sludge removal period was the main parameter for determination of the HRT. At such HRT, both COD removal and wastewater conversion are also optimised. The model results demonstrated that for treatment of faeces in an accumulation (AC) system at temperature > or = 25 degrees C, the filling period of the system should be higher than 60 days. For maximisation of the net biogas production (i.e. reduction of biogas losses as dissolved in the effluent), the separation between grey water, urine and faeces and reduction of water consumption for faeces flushing are required. Furthermore, the faeces and kitchen organic wastes and grey water are digested in, respectively, an AC system and UASB reactor, while the urine is stored.     

Real-time quantifications of dominant anaerobes in an upflow reactor by polymerase chain reaction using a TaqMan probe.

This study was conducted to demonstrate the application of quantitative real-time polymerase chain reaction (qRT-PCR) for the quantification of dominant bacteria in an anaerobic reactor using a designed TaqMan probe. A novel group of uncultured thermophilic bacteria affiliated with Thermotogales was first found in a phenol-degrading sludge from a 55 degrees C upflow anaerobic sludge blanket (UASB) reactor, which effectively removed 99% of phenol at loading of 0.51 g-phenol l(-1) d(-1) h of hydraulic retention. A TaqMan probe was then designed targeting this group of Thermotogales affiliated bacteria (TAB), and used to monitor its concentration in the reactors. Results showed that the TAB population in the 55 degrees C reactor increased proportional to the phenol degrading rate. Results also showed that the TAB population ranged 3.5-9.9% in the 55 degrees C phenol-degrading sludge, but only 0.0044% in the 37 degrees C sludge and 0.000086% in the 26 degrees C sludge.     

Pretreatment of silk-dyeing industrial wastewater by UASB reactor.

The objective of this study was to investigate the performance of the upflow anaerobic sludge blanket (UASB) reactor as the pretreatment system for silk-dyeing wastewater. Two laboratory-scale UASB reactors, with working volume of 15.59 I, were used during May 1998 to June 1999. The actual wastewater was diluted to reduce ammonium ion toxicity on anaerobic bacteria. The experiments were conducted at the organic loading rates (OLRs) of 0.52, 1.01, 1.04, 1.54 and 2.56 kgCOD/(m3 x d), treating only wastewater generated from the acid-dye process of mixed-species raw silk. It took approximately 4 1/2 months to reach the steady-state conditions. It was found that the COD removal was in the ranges of 74.1-85.3%, except at OLR 2.56 kgCOD/(m3 x d) where efficiency significantly dropped to 55.2%. The apparent color removal was in the similar trend as COD. During the study periods, wastewater input had various color shades while the effluent generally looked pale yellowish. The methane generation rates ranged from 0.18-0.31 m3/kg COD removed, with methane composition 81.0-88.1% in biogas. The average granule size in the sludge bed had slowly increased to 0.73 mm in the last experiment. It can be concluded that the UASB reactor is suitable as a pretreatment system for silk-dyeing wastewater. An OLR of 1 kgCOD/(m3 x d) and an influent concentration diluted to 2,600 mgCOD/l are suggested while COD and apparent color removal efficiency of 80% and 70%, respectively, can be expected.     

Thermal hygienization of excess anaerobic sludge: a possible self-sustained application of biogas produced in UASB reactors.

The main current trends in final disposal of sludge from Wastewater Treatment Plants (WTP) include: safe use of nutrients and organic matter in agriculture, sludge disinfection and restricted use in landfill. As to sludge hygienization, helminth eggs have been used as a major parameter to determine the effectiveness of such process, and its inactivation can be reached by means of thermal treatment, under varying temperature and other conditions. In such context, the objective of this research was to determine how effectively biogas produced in UASB reactors could be used as a source of calorific energy for the thermal hygienization of excess anaerobic sludge, with Ascaris lumbricoides eggs being used as indicator microorganisms, and whether the system can operate on a self-sustained basis. The experiments were conducted in a pilot-scale plant comprising one UASB reactor, two biogas holders and one thermal reactor. The investigation proved to be of extreme importance to developing countries, since it leads to a simplified and fully self-sustainable solution for sludge hygienization, while making it possible to reuse such material for agricultural purposes. It should be also noted that using biogas from UASB reactors is more than sufficient to accomplish the thermal hygienization of all excess sludge produced by this system, when used for treating domestic sewage.     

Nutrient removal and microbial granulation in an anaerobic process treating inorganic and organic nitrogenous wastewater.

The sustainable anaerobic nitrogen removal and microbial granulation were investigated by using a laboratory anaerobic granular sludge bed reactor, treating synthetic (inorganic and organic) wastewater and piggery waste. From inorganic synthetic wastewater, lithoautotrophic ammonium oxidation to nitrite/nitrate was observed by an addition of hydroxylamine. Also, the results revealed that the Anammox intermediates (particularly, hydrazine) contents in the substrate would be one of the important parameters for success of the anaerobic nitrogen removal process. The results from organic synthetic wastewater show that if the Anammox organism were not great enough in the startup of the process, denitritation and anaerobic ammonification would be a process prior to the Anammox reaction. The anaerobic ammonium removal from the piggery waste was performed successfully, probably due to the Anammox intermediates contained in the substrate. This reactor shows a complex performance including the Anammox reaction and HAP crystallization, as well as having partial denitritation occurring simultaneously. From the activity test, the maximum specific N conversion rate was 0.1 g NH4-N/g VSS/day (0.77 g T-N/g VSS/day), indicating that potential denitritation is quite high. The NO2-N/NH4-N ratio to Anammox is 1.17. The colour of the biomass treating the piggery waste changed from black to dark red. It was also observed that the red-colored granular sludge had a diameter of 1-2 mm. The settleability assessment of the granular sludge revealed that the granular sludge had a good settleability even though it was worse than that of seed granular sludge.     

Impact of high saline wastewaters on anaerobic granular sludge functionalities.

Three UASB reactors were operated at different salinity levels in order to assess the effects on the granular sludge properties. High levels of activity inhibition were observed at sodium concentrations over 7 g Na(+)/L, which resulted in low applicable organic loading rates and VFA accumulation in reactor effluents. However, either sludge adaptation or selection for saline resistant microorganisms occurred, which could be concluded from the observed increase in the 50% activity inhibitory concentrations of sodium during continuous flow experiments. Changes in Na(+) susceptibility in time are likely to be expected when treating saline wastewaters. The latter was evidenced by the high sodium tolerance of granular methanogenic sludge coming from a full-scale industrial reactor treating such wastewater. High salinity conditions resulted in a reduced granule strength, predicting process instabilities during long term reactor operation. Batch tests showed that high sodium concentrations seemed to displace the calcium from the granular sludge, a factor known to affect anaerobic granules formation.     

Co-degradation of phenol and m-cresols by upflow anaerobic sludge blanket reactor.

The study was performed to assess the efficacy of an upflow anaerobic sludge blanket reactor for the degradation of mixtures of phenol and m-cresol. The experiments were performed in an upflow anaerobic sludge blanket reactor. The reactor was seeded with digested sewage sludge and was initially operated at 24 HRT. A phenol concentration of 200 mg/L was fed to the reactor to acclimatize the microorganisms to phenols. Subsequently the dosages of phenols were increased to 400 mg/L, 500 mg/L, and 600 mg/L. Cresols were introduced in the reactor when phenol removal efficiency of 77% was achieved at phenol concentration of 600 mg/L. Different phenol to m-cresol ratios were tried and the performance of the reactor was evaluated for each case. The result demonstrates that it is important to consider phenol/ m-cresol ratio to avoid toxic effects and both can be co-degraded successfully under anaerobic conditions provided proper acclimatization time is given.     

The impact of metal transport processes on bioavailability of free and complex metal ions in methanogenic granular sludge

Bioavailability of metals in anaerobic granular sludge has been extensively studied, because it can have a major effect on metal limitation and metal toxicity to microorganisms present in the sludge. Bioavailability of metals can be manipulated by bonding to complexing molecules such as ethylenediaminetetraacetate (EDTA) or diethylenetriaminepentaacetate (DTPA). It has been shown that although the stimulating effect of the complexed metal species (e.g. [CoEDTA](2-)) is very fast, it is not sustainable when applied to metal-limited continuously operated reactors. The present paper describes transport phenomena taking place inside single methanogenic granules when the granules are exposed to various metal species. This was done using magnetic resonance imaging (MRI). The MRI results were subsequently related to technological observations such as changes in methanogenic activity upon cobalt injection into cobalt-limited up-flow anaerobic sludge blanket (UASB) reactors. It was shown that transport of complexed metal species is fast (minutes to tens of minutes) and complexed metal can therefore quickly reach the entire volume of the granule. Free metal species tend to interact with the granular matrix resulting in slower transport (tens of minutes to hours) but higher final metal concentrations.     

Alkaline and acid hydrolytic processes in aerobic and anaerobic sludges: effect on total EPS and fractions.

Sludge samples from an upflow anaerobic sludge blanket (UASB) reactor and four submerged aerated biofilters (BFs) of a wastewater treatment plant (1,000 inhab.) were processed at bench scale by alkaline and acid hydrolysis with the objective to evaluate the organic matter solubilization, volatile solids (VS) destruction and the effect of hydrolytic processes on the extracellular polymeric substances (EPS) fraction of the sludge samples. The results showed that alkaline hydrolysis of sludge samples treatment with 1.0% total solids (TS) using NaOH 20 meq L(-1) was more efficient on organic matter solubilization and VS destruction than acid hydrolysis. The EPS sludge content was also affected by the alkaline treatment of anaerobic sludge samples. The EPS concentrations (mg EPS/gVSS) on the anaerobic sludge after the alkaline treatment were significantly lowered according to sample height in the UASB reactor. Data indicated that the EPS sludge fraction is the main component affected by the alkaline hydrolytic process of anaerobic sludge samples.