Development of granular sludge for textile wastewater treatment

Microbial granular sludge that is capable to treat textile wastewater in a single reactor under intermittent anaerobic and aerobic conditions was developed in this study. The granules were cultivated using mixed sewage and textile mill sludge in combination with anaerobic granules collected from an anaerobic sludge blanket reactor as seed. The granules were developed in a single sequential batch reactor (SBR) system under alternating anaerobic and aerobic condition fed with synthetic textile wastewater. The characteristics of the microbial granular sludge were monitored throughout the study period. During this period, the average size of the granules increased from 0.02 ± 0.01 mm to 2.3 ± 1.0 mm and the average settling velocity increased from 9.9 ± 0.7 m h⁻¹ to 80 ± 8 m h⁻¹. This resulted in an increased biomass concentration (from 2.9 ± 0.8 g L⁻¹ to 7.3 ± 0.9 g L⁻¹) and mean cell residence time (from 1.4 days to 8.3 days). The strength of the granules, expressed as the integrity coefficient also improved. The sequential batch reactor system demonstrated good removal of COD and ammonia of 94% and 95%, respectively, at the end of the study. However, only 62% of color removal was observed. The findings of this study show that granular sludge could be developed in a single reactor with an intermittent anaerobic-aerobic reaction phase and is capable in treating the textile wastewater.     

Methanogenic granular sludge as a seed in an anaerobic baffled reactor

This paper reviews the importance of phase separation in anaerobic wastewater treatment, characteristics of anaerobic baffled reactor (ABR), properties of anaerobic granular sludge, granulation process and advantages of granular sludge over nongranular sludge. The performance data of ABR and its modified configurations with regard to carbonaceous matter removal by using various seed sludges are compared. It is concluded that enhanced wastewater treatment efficiencies can be achieved with methanogenic granular seed sludge in an ABR because of a number of advantages associated with granular biomass over nongranular aggregates.     

Removal of organic acids by activated sludges

Removal of coexisted volatile organic acids was studied using three kinds of activated sludges; treated with sewage, digested night soil and undiluted night soil at the plant scale and laboratrial experiment. Concentration of volatile fatty acids in sewage were too low to be detected, meanwhile 5–28 ppm of acetic acid were detected in influent of aeration tank of digested night soil treatment plant, and 1335–5340 ppm of acetic acid were detected in night soil. Removal rates of acetic acid were 35.9 mg g⁻¹ h⁻¹ by sewage activated sludge, 33.6 mg g⁻¹ h⁻¹ by digested night soil activated sludge and 16.9 mg g⁻¹ h⁻¹ by undiluted night soil activated sludge under coexisting volatile fatty acids. This difference depends on the number of bacteria in the activated sludge. Dissimilation percentage of acetic, propionic, butyric and valeric acids were similar results in these activated sludges.     

Degradation of phenol in wastewater in an upflow anaerobic sludge blanket reactor

Phenol in wastewater could be effectively degraded in an upflow anaerobic sludge blanket (UASB) reactor. With a 1:1 effluent recycle ratio, over 97% of phenol was removed at 37°C and pH 6.9-7.5 with 12 h of hydraulic retention time for phenol concentration up to 1260 mg·1⁻¹, corresponding to 3000 mg·1⁻¹ of chemical oxygen demand (COD) and a loading rate of 6 g-COD·1⁻¹·day⁻¹. The seed sludge took about 7 wk to develop the phenol-degrading capability which was sensitive to shocks. The bioactivity deteriorated readily when the granules were exposed to sudden changes of temperature and loading. Although the damage was not permanent, the recovery of bioactivity was gradual and lengthy. At 6 g-COD·1⁻¹·day⁻¹, each gram of granules was able to convert 0.49 g of COD into methane daily. On the average, about 94.7% of the total COD removed was converted to methane, while the rest was converted to biomass with a net yield of 0.038 g-VSS·(g-COD-removed)⁻¹. Electron micrographs show that the granules were composed of, among others, Syntrophus buswellii-, Methanothrix-, Methanospirillum- and Methanobrevibacter-like bacteria.     

Thickening of waste activated sludge by biological flotation

Waste activated sludge was thickened by biological flotation without polymer flocculant dosage. The BIOFLOT® process utilizes the denitrifying ability of activated sludge bacteria. Gaseous products of anaerobic nitrate reduction cause spontaneous flotation of the sludge suspended solids. Laboratory tests confirmed the dependence of sludge thickening efficiency on available nitrate concentration, flotation time and temperature. Full-scale experiments were performed in a fully automatized unit for discontinuous sludge thickening from wastewater treatment plants with a capacity of up to 5000 I.E. Waste activated sludge from wastewater treatment plants at Pisek. Milevsko and Björnlunda was thickened from 6.2, 10.7 and 3.5 g/l MLSS to 59.4, 59.7 and 66.7 g/t MLSS, respectively. Concentrations of COD, ammonium and phosphate ions were decreased in sludge water. The average nitrate consumption for bioflotation was 21.2 mg NO₁⁻ per 1 g of MLSS of activated sludge. Flotation time ranged from 4 to 48 h.     

Effect of temperature on the anaerobic thermophilic conversion of volatile fatty acids by dispersed and granular sludge

The effect of temperature on the rate of volatile fatty acid (VFA) conversion by thermophilic methanogenic sludge, cultivated at 55°C, was studied using both batch activity tests and continuous flow experiments. The temperature dependence of acetate conversion in the range between 37–70°C could be described by an Arrhenius derived model when dispersed sludge with a low specific activity was used. For this sludge the optimum acetate conversion rate was found at 65°C. However, the maximum acetate utilization rate was not affected by temperature in the range between 50°C to 65°C when granular sludge with a high specific methanogenic activity was used. Crushing the granules led to a 2 to 3 fold increase in the maximum activity at 60–65°C, indicating that the conversion rate was very likely limited by the diffusion rate of acetate into the granules. Similar results were obtained with butyrate as the substrate. The temperature dependence of the crushed granules was similar to that of the less active dispersed sludge. In contrast, the thermophilic propionate oxidation rate was highest with the intact granular sludge while a similar temperature dependence was found for both the granular and dispersed sludges. The affinity for VFA increased with decreasing temperature. This phenomenon was most pronounced for the granular sludge. The thermophilic treatment of a VFA-mixture in a UASB reactor appeared to be only slightly affected by temperature when moderately low loading rates were applied, i.e. 20 kg COD·m⁻³·d⁻¹. However, temperature had a strong effect applying loading rates of 40–90 kg COD·m⁻³·d⁻¹ accompanied with high effluent VFA concentrations. The results reveal a high thermostability of the thermophilic wastewater treatment process in the range 45–60°C if “high-rate” reactors with a granular sludge bed are used.     

Extracellular polymeric substances (EPS) in upflow anaerobic sludge blanket (UASB) reactors operated under high salinity conditions

Considering the importance of stable and well-functioning granular sludge in anaerobic high-rate reactors, a series of experiments were conducted to determine the production and composition of EPS in high sodium concentration wastewaters pertaining to anaerobic granule properties. The UASB reactors were fed with either fully acidified substrate (FAS) consisting of an acetate medium (reactor R1) or partly acidified substrate (PAS) consisting of acetate, gelatine and starch medium (reactors R2, R3, and R4). For EPS extraction, the cation exchange resin (CER) method was used. Strength and particle size distribution were determined by assessing the formation of fines sludge under conditions of high shear rate and by laser diffraction, respectively. Batch tests were performed in 0.25 L bottles to study Ca²⁺ leaching from anaerobic granular sludge when incubated in 20 g Na⁺/L in the absence of feeding for 30 days. Results show a steady increase in the bulk liquid Ca²⁺ concentration during the incubation period. UASB reactor results show that the amounts of extracted proteins were higher from reactors R2 and R3, fed with PAS compared to the sludge samples from reactor R1, fed with FAS. Strikingly, the amount of extracted proteins also increased for all reactor sludges, irrespective of the Na⁺ concentration applied in the feed, i.e. 10 or 20 gNa⁺/L. PAS grown granular sludges showed an important increase in particle size during the operation of the UASB reactors. Results also show that, addition of 1 gCa²⁺/L to the high salinity wastewater increases the granules' strength.     

Effect of extended idle conditions on structure and activity of granular activated sludge

In industry and in tourist areas, periods exist during which no or only very little sewage is produced, and the wastewater treatment facilities have to be set into an idle phase over several days and even weeks. When wastewater is generated again and delivered to the treatment plant, the microorganisms in the activated sludge plant may have lost activity, and the activated sludge flocs may have disintegrated. From previous observation, it is assumed that granular activated sludge is more resistant against long-term storage than activated sludge flocs. Experiments using a laboratory-scale sequencing batch reactor (SBR) were conducted to study the impacts of a 7-weeks anaerobic idle time on structural integrity and metabolic activity of granular activated sludge, and the time required to regain the former operational status of the plant. Oxygen consumption rate (OCR) was used as an indicator to evaluate the metabolic activity of the sludge. The results revealed that the size, color and sedimentation characteristics of the granular sludge did hardly change during the storage period. Sludge activity, however, dropped to values as low as 0.17 mg min(-1)L(-1). After restarting the reactor, the OCR increased within 1 day to a level of 0.57 mg min(-1)L(-1), kept rising at a linear rate in the following days, and reached after 1 week, a value of 5.74 mg min(-1)L(-1) typical for the former activity status. These results imply that granular activated sludge can be stored for a considerably long period of time, and brought into service again relatively quickly. After an idle period of 7 weeks, it took less than a week to regain full capacity of the SBR.     

A survey of municipal anaerobic sludge digesters and diagnostic activity assays

A plant site survey was made of 30 municipal wastewater treatment plants concerning the operational characteristics of their anaerobic sludge digesters. Design information, operating data and analytical data were tabulated. Samples of each sludge were then assayed to determine the residual gas production rate, the maximum potential acetate and propionate utilization rates, the 5 and 30 day biochemical methane potential (BMP₅) (BMP₃₀) and the possible limitation in bioavailability of iron, cobalt or nickel.The average solids content of the raw sludge fed to the digesters was 4. 7%. Eight of the 30 sludges showed stimulation in the gas production rate when iron, cobalt or nickel was supplemented and acetate was unlimiting. Nine of the 30 sludges showed stimulation in the gas production rate when iron, cobalt or nickel was supplemented and propionate was unlimiting.The average BMP₅ was 0. 7 volumes of methane per volume of sludge. The average BMP₃₀ was 1.9 vol CH₄/vol sludge. On average 87% of the biodegradable fraction of the sludge was converted to methane during digestion. The average maximum potential acetate utilization rate (MPAUR) was 0.93 vol CH₄/vol sludge-day. The average maximum potential propionate utilization rate (MPPUR) was 0.18 vol CH₄ /vol sludge-day. The average H₂S in the digester gas was 2200 ppm. The average digester capacity was 0.14 million gallons/million gallons per day (MG/MGD) of raw wastewater. On average the raw sludge pumping rate was 4300 gal per MG of raw wastewater. The average digester gas production was 0.066 vol gas/vol of raw wastewater (8800 ft³ per MG). The average unit gas production rate was 0. 64 volumes of digester gas per volume of digester per day. The average volume of digester gas produced per volume of raw sludge feed was 15. 8 v/v. The average gas production per pound of volatile solids added was 0. 46 m³ kg⁻¹ VS (7. 4 ft³ lb⁻¹ VS). The average gas production per pound of volatile solids destroyed was 0. 94 m³ kg⁻¹ VS (15. 0 ft³ lb⁻¹ VS).     

A ferricyanide-mediated activated sludge bioassay for fast determination of the biochemical oxygen demand of wastewaters

Activated sludge was successfully incorporated as the biocatalyst in the fast, ferricyanide-mediated biochemical oxygen demand (FM-BOD) bioassay. Sludge preparation procedures were optimized for three potential biocatalysts; aeration basin mixed liquor, aerobic digester sludge and return activated sludge. Following a 24 h starving period, the return activated sludge and mixed liquor sludges reported the highest oxidative degradation of a standard glucose/glutamic acid (GGA) mixture and the return activated sludge also recorded the lowest endogenous FM-respiration rate. Dynamic working ranges up to 170 mg BOD₅ L⁻¹ for OECD standard solutions and 300 mg BOD₅ L⁻¹ for GGA were obtained. This is a considerable improvement upon the BOD₅ standard assay and most other rapid BOD techniques. Time-series ferricyanide-mediated oxidation of the OECD¹⁷⁰ standard approached that of the GGA¹⁹⁸ standard after 3–6 h. This is noteworthy given the OECD standard is formulated as a synthetic sewage analogue. A highly significant correlation with the BOD₅ standard method (n = 35, p < 0.001, R = 0.952) was observed for a wide diversity of real wastewater samples. The mean degradation efficiency was indistinguishable from that observed for the BOD₅ assay. These results demonstrate that the activated sludge FM-BOD assay may be used for simple, same-day BOD analysis of wastewaters.     

Interactions between methanogenic,sulfate-reducing and syntrophic acetogenic bacteria in the anaerobic degradation of benzoate

Effect of sulfate on the anaerobic degradation of benzoate was investigated by using the chemostat-type reactors at 35°C. The benzoate concentrations were equivalent to 1250–10000 mg.l⁻¹ in COD (chemical oxygen demand) and the sulfate concentrations were equivalent to 167–1670 mg.l⁻¹ in sulfur (S). Interactions between the methane-producing bacteria (MPB) and sulfate-reducing bacteria (SRB) were dependent strongly on the ratio of COD/S in wastewater. The MPB consumed 99% of the available electron donors at COD/S ratio of 60, but consumed only 69% at ratio of 1.5, and 13% at 0.75. The biochemical reactions and the bacterial composition in the biomass were also governed by the COD/S ratio. At high COD/S ratios (3.0 or higher), benzoate was degraded mainly to methane via acetate and hydrogen/formate. The degradation of benzoate required the syntrophic association between the hydrogen-producing acetogens such as Syntrophus buswellii and hydrogen-consuming MPB, plus Methanothrix-like MPB. On the other hand, at low COD/S ratio (1.5 or lower), benzoate was consumed mainly by SRB, converting sulfate into sulfide and suppressing the methane production. The anaerobic degradation of benzoate was partially inhibited when sulfide concentration was high.     

好氧颗粒污泥技术用于味精废水处理的研究

以厌氧颗粒污泥为接种污泥,采用人工模拟废水在SBR反应器内培养好氧颗粒污泥,35 d后颗粒污泥成熟,反应器对COD和NH4+-N的去除率分别高于95%和99%。采用该反应器处理味精废水,当COD、NH4+-N的容积负荷分别为2.4、0.24 kg/(m3.d)时,对COD、NH4+-N和TN的去除率分别在90%、99%和85%左右,且颗粒污泥未出现解体的现象。以厌氧颗粒污泥为接种污泥、味精废水为进水,在与上述相同条件下培养好氧颗粒污泥,经过60 d的培养,反应器内的污泥以絮状污泥为主,该系统对COD、NH4+-N和TN的去除率分别为85%、99%和70%。     

Bacterial response to a shock load of nanosilver in an activated sludge treatment system

The growing release of nanosilver into sewage systems has increased the concerns on the potential adverse impacts of silver nanoparticles (AgNPs) in wastewater treatment plants. The inhibitory effects of nanosilver on wastewater treatment and the response of activated sludge bacteria to the shock loading of AgNPs were evaluated in a Modified Ludzack-Ettinger (MLE) activated sludge treatment system. Before shock-loading experiments, batch extant respirometric assays determined that at 1 mg/L of total Ag, nitrification inhibitions by AgNPs (average size = 1-29 nm) and Ag⁺ ions were 41.4% and 13.5%, respectively, indicating that nanosilver was more toxic to nitrifying bacteria in activated sludge than silver ions. After a 12-h period of nanosilver shock loading to reach a final peak silver concentration of 0.75 mg/L in the MLE system, the total silver concentration in the mixed liquor decreased exponentially. A continuous flow-through model predicted that the silver in the activated sludge system would be washed out 25 days after the shock loading. Meanwhile, a prolonged period of nitrification inhibition (>1 month, the highest degree of inhibition = 46.5%) and increase of ammonia/nitrite concentration in wastewater effluent were observed. However, nanosilver exposure did not affect the growth of heterotrophs responsible for organic matter removal. Microbial community structure analysis indicated that the ammonium-oxidizing bacteria and nitrite-oxidizing bacteria, Nitrospira, had experienced population decrease while Nitrobacter was washed out after the shock loading.     

Cell wash-out and external mass transfer resistance in horizontal-flow anaerobic immobilized sludge reactor

Polyurethane foam has been studied as a support for anaerobic sludge immobilization in packed-bed bioreactors. Studies about fundamental aspects in reactors containing immobilized sludge in such a type of support must be carried out to permit simulation and optimization of their performance and to provide parameters for safe scale-up. The effect of the liquid superficial velocity on the wash-out of anaerobic biomass and the evaluation of the external mass transfer resistance are presented in this paper. The polyurethane foam cubic matrices were taken from a bench-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating kraft paper industry wastewater submitted to eight different water flow rates in a 10 ml tube segment for cell wash-out evaluation and six different glucose solution flow rates in a 10 ml differential reactor for external mass transfer resistance evaluation. There was a significant wash-out of total suspended solids (23%) but only 9% of volatile suspended solids were washed-out from polyurethane foam matrices when they were subjected to liquid superficial velocities ranging from 0.30 to 2.21 cm.s⁻¹. The external mass transfer resistance decreased with the increase in liquid superficial velocity, but the condition of minimum resistance was not obtained in the applied v_s range (0.007–0.075 cm.s⁻¹).     

Integration of anammox into the aerobic granular sludge process for main stream wastewater treatment at ambient temperatures

Anaerobic ammonium oxidation, nitrification and removal of COD was studied at ambient temperature (18 °C ± 3) in an anoxic/aerobic granular sludge reactor during 390 days. The reactor was operated in a sequencing fed batch mode and was fed with acetate and ammonium containing medium with a COD/N ratio of 0.5 [g COD/gN]. During influent addition, the medium was mixed with recycled effluent which contained nitrate in order to allow acetate oxidation and nitrate reduction by anammox bacteria. In the remainder of the operational cycle the reactor was aerated and controlled at a dissolved oxygen concentration of 1.5 mg O₂/l in order to establish simultaneous nitritation and Anammox. Fluorescent in-situ hybridization (FISH) revealed that the dominant Anammox bacterial population shifted toward Candidatus “Brocadia fulgida” which is known to be capable of organotrophic nitrate reduction. The reactor achieved stable volumetric removal rates of 900 [g N₂-N/m³/day] and 600 [g COD/m³/day]. During the total experimental period Anammox bacteria remained dominant and the sludge production was 5 fold lower than what was expected by heterotrophic growth suggesting that consumed acetate was not used by heterotrophs. These observations show that Anammox bacteria can effectively compete for COD at ambient temperatures and can remove effectively nitrate with a limited amount of acetate. This study indicates a potential successful route toward application of Anammox in granular sludge reactors on municipal wastewater with a limited amount of COD.     

Basic studies on carbon dioxide/air control system for activated sludge processes

Basic facts about the production of carbon dioxide by activated sludge in an aeration tank were gathered with a continuous-flow-type apparatus, and the dynamic characteristics of activated sludge was analyzed with a batch-type aeration tank. In addition, a carbon dioxide/air control system was designed and applied to an activated sludge pilot plant, where the carbon dioxide in exhausted air was continuously measured with an infrared analyzer. The control system maintained the carbon dioxide concentration in exhausted air within ± 0.005 vol%, with a typical diurnal flow rate pattern in sewage, and maintained the oxygen content in mixed liquor within ± 0.4 mg l⁻¹.     

Volatile solids reduction in two-phase and conventional anaerobic sludge digestion

Success of two-phase anaerobic systems for primary and secondary sludge treatment has been reported based on both directly and indirectly measured volatile solids (VS) reduction, total gas and methane generation, COD reduction, etc. The objective of this research was to determine whether phase separation increases directly measured VS reduction compared to conventional anaerobic sludge digestion. Two-phase and conventional digesters were operated with sludge feeds from three sources; both 1:1 sludges (primary:waste activated, solids basis) and 100% waste activated sludges (WAS) were studied. The maximum difference between VS reductions in conventional and two-phase systems was about 8.7% with waste activated sludge. The increase in volatile solids reduction in two-phase systems with the 1:1 sludge ranged from 1.9 to 6.0% as compared to conventional systems. This relatively small increase in VS reduction may not be worth the additional cost of operating two-phase digesters at full scale.     

光合细菌/活性污泥工艺处理高盐染料废水的研究

采用厌氧酸化、陶粒挂膜的光合细菌(简称PSB)和组合填料挂膜的活性污泥组合技术处理高盐染料废水,考察了其除污效果以及PSB池在流程中的位置对去除污染物的影响.结果表明:随着含盐量和COD浓度的增加,PSB/活性污泥工艺和活性污泥/PSB工艺对高盐染料废水的处理效果均下降.当含盐量为2%、COD为4 000 mg/L左右时,两工艺对COD的平均去除率分别为90.9%和85.1%,对氨氮的平均去除率分别为9.3%和9.7%,对总氮的平均去除率分别为15.5%和15.6%,脱色率分别为90.9%和89.2%.可见,PSB/活性污泥工艺对COD和色度的去除效果更好,适合处理高盐染料废水.     

Activated sludge treatment of abattoir wastewater—II : Influence of dissolved oxygen concentration

Performance of laboratory scale completely mixed activated sludge reactors fed with abattoir wastewater was measured at different dissolved oxygen (DO) concentrations. Degradation of fat present in the influent was inhibited at DO concentrations below about 0.5 mg l⁻¹, leading to sludges with high fat content which settled poorly due to excessive numbers of filamentous microorganisms. Fat was degraded rapidly at higher DO concentrations (up to 4.0 mg l⁻¹) and the sludge contained few filamentous microorganisms, a low fat content and settled readily. However, effluent quality was highest at low DO concentrations due to lower levels of soluble breakdown products from the fat.When wastewater was fed intermittently at constant aeration rate, sludge with a low fat content and good settleability resulted, even though the DO concentration was about 0.2 mg l⁻¹ for more than 30% of the time. Effluent quality was also high. Thus it is concluded that for full-scale abattoir treatment plants where wastewater flow is intermittent, DO concentration may be low during periods of high loading without adversely affecting effluent quality or sludge settleability.     

Nitrogen and phosphorus removal from an abattoir wastewater in a SBR with aerobic granular sludge

The formation and performance of granular sludge was studied in an 8 l sequencing batch reactor (SBR) treating an abattoir (slaughterhouse) wastewater. Influent concentrations averaged 1520 mg l⁻¹ volatile suspended solids (VSS), 7685 mg l⁻¹ Chemical oxygen demand (COD), 1057 mg l⁻¹ total kjeldahl nitrogen (TKN), 217 mg l⁻¹ total P. The COD loading was 2.6 kg m⁻³ d⁻¹. The SBR was seeded with flocculating sludge from a SBR with an 1 h settle time, but granules developed within 4 days by reducing the settle time to 2 min. The SBR cycle also had 120 min mixed (anaerobic) fill, 220 min aerated react, and 18 min draw/idle. The granules had a mean diameter of 1.7 mm, a specific gravity of 1.035, a density of 62 g VSS l⁻¹, a zone settling velocity (ZSV) of 51 m h⁻¹, and a sludge volume index (SVI) of 22 ml g⁻¹. Without optimizing process conditions, removal of COD and P were over 98%, and removal of N and VSS were over 97%. Nitrification and denitrification occurred simultaneously during react. The results indicate that conventional SBRs treating wastewaters with flocculating sludge can be converted to granular SBRs by reducing the settle time.