Treatment of low strength domestic wastewater using the anaerobic filter

A laboratory scale anaerobic filter packed with synthetic high surface area trickling filter media was used to treat a low strength domestic wastewater averaging 288 mg 1⁻¹ COD. The filter was operated for 60 days after reaching steady-state at 20, 25, 35°C at a loading rate of 0.02 lb COD ft⁻³ day⁻¹ and 24 h hydraulic retention time. Filter effluent BOD₅ averaged 38 mg 1⁻¹ providing an average removal rate of 79%, and effluent COD averaged 78 mg 1⁻¹, corresponding to a 73% removal rate. Removal efficiencies showed very little sensitivity to daily fluctuations in influent wastewater quality. The filter performance at 25 and 35°C was not significantly different, but BOD and TSS removal efficiency declined a: 20°C. Gas production averaged 0.027 ft⁻³ of gas per ft³ of influent wastewater, or 1.875 ft³ of gas per pound of influent COD. Gas composition averaged 30% nitrogen, 65% methane, and 5% carbon dioxide. Ammonia nitrogen and sulfides both increased during treatment. It is concluded that the anaerobic filter is a promising candidate for treatment of low strength wastewaters and that post treatment for sulfides and ammonia may be necessary.     

Combined biological treatment of high‐sulphate wastewater from yeast production

The wastewater from baker's yeast production contains above‐average concentrations of organic pollutants (25 000 mg/L total chemical oxygen demand, TCOD), nutrients (1500 mg/L N_tot, 100 mg/L P_tot) and sulphate (2900 mg/L SO₄^2?). Baker's yeast wastewater with a flow rate of 190 m³/day was treated in a mesophilic anaerobic/anoxic continuous stirred tank reactor (CSTR) system. At the expense of the reduction of trimethylglycine (or betaine‐component of sugar‐beet molasses) to other nitrogen‐containing compounds, it was possible to re‐oxidize the sulphides to elemental sulphur, remove them from the wastewater and increase biogas production. Therefore, the average removal efficiency in the anaerobic/anoxic system was 79% by TCOD, 100% by SO₄^2? in which the concentration of sulphides in the effluent did not exceed 50 mg/L. The application of this combined anaerobic/anoxic system to a full‐scale treatment plant supported biogas production up to 1300 m³/day, and the purification of wastewater was feasible without the use of granular sludge.     

The activated sludge process—IV: Application of the general kinetic model to anoxic-aerobic digestion of waste activated sludge

This paper discusses the application of the general activated sludge model as set out by Dold et al. (Prog. Wat. Technol.12, 47–77, 1980) and extended by Van Haandel et al. (Wat. Res.15, 1135–1152, 1981), to anoxic-aerobic digestion of waste activated sludge. The laboratory scale experimental investigation comprised a 6 day sludge age activated sludge process, the waste sludge from which was fed to a number of digesters operated as follows: single reactor flow-through digesters at 4 or 10 days sludge age (retention times) under aerobic or anoxic-aerobic conditions (with 1.5 and 4 h cycle times) and 3-in-series flow-through aerobic digesters each with 4 days sludge age; all digesters were fed draw-and-fill wise once per day. The general kinetic model simulated accurately all the experimental data without the need to change the values of the kinetic constants. Both theoretical simulations and experimental data indicate that (i) the rate of volatile solids destruction is not affected by the incorporation of anoxic cycles and (ii) the specific denitrification rate constant in a digester is about two-thirds of that in the secondary anoxic reactor of the single sludge activated sludge system; this allows definition of a fourth denitrification rate constant K₄ for the anoxic-aerobic digester with K₄T = 0.046(1.029)^(T-20) mg(NO₃-N) (mgAVSS d)⁻¹, a constant independent of sludge age. An important consequence of (i) and (ii) above is that the denitrification can be integrated readily into the steady state digester model of Marais and Ekama (Wat. SA2, 163–200, 1976) and used for design purposes.     

Pre-treatment mechanisms during thermophilic-mesophilic temperature phased anaerobic digestion of primary sludge

Pre-treatment is used extensively to improve degradability and hydrolysis rate of material being fed into digesters. One emerging process is temperature phased anaerobic digestion (TPAD), which applies a short (2 day) 50-70 °C pre-treatment step prior to 35 °C digestion in the main stage (10-20 days). In this study, we evaluated a thermophilic-mesophilic TPAD against a mesophilic-mesophilic TPAD treating primary sludge. Thermophilic-mesophilic TPAD achieved 54% VS destruction compared to 44% in mesophilic-mesophilic TPAD, with a 25% parallel increase in methane production. Measurements of soluble COD and NH₄⁺-N showed increased hydrolysis extent during thermophilic pre-treatment. Model based analysis indicated the improved performance was due to an increased hydrolysis coefficient rather than an increased inherent degradability, suggesting while TPAD is suitable as an intensification process, a larger main digester could achieve similar impact.     

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.     

超声/碱预处理剩余污泥的中温厌氧消化效果

考察了超声/碱联合预处理对剩余污泥中温厌氧消化的影响,并与原污泥直接进行厌氧消化的效果进行了比较.试验结果表明,在高投配率(10%)下原污泥直接进行厌氧消化对有机物的去除率不高,经过超声/碱预处理后,消化过程中对TCOD的去除率提高了29.6%,单位污泥的日均产气量提高了67.9%,对VS和VSS的去除率分别提高了58.9%和28.6%.     

Research of parameters affecting sludge digestion process

The parameters characterizing and affecting anaerobic sludge digestion process in three Lithuanian cities are investigated. Results showed that digestion process was effective in all three objects: specific biogas production varied between 0.77 and 0.86 m³/kg volatile solids destroyed, methane content in the biogas varied between 64 and 67% and they complied with the values presented in the scientific references. The increase of VS loading (up to 2.6 kg VS/m³/day) led to the higher level of VS destruction which was up to 59%. The sludge retention time (hydraulic retention time) values must be in ranges of 20–25 days for the digestion process in order to get the design VS destruction, as well the biogas production. In a case of lack of raw materials, the application of wastes from food industry can help to reach the design parameters. The application of wastes from milk industry showed positive results in the digestion process.     

Operating Experiences of Sludge Disinfection and Stabilization at Colburn Sewage Treatment Works, Yorkshire

A NEW integrated sludge treatment plant was installed at Colburn sewage treatment works (STW) in 1986. The plant comprises a number of novel features including a continuous gravity thickener features including a continuous gravity thickener, a pasteurization unit using submerged combustion of digester gas for sludge heating, a peat-bed odour control system, and a 'pump-our/pump-in'prefabricated anaerobic digester. Plant operation is controlled automatically by a computer system The performance of the thickener has been in accordance with predictions and has achieved at least a halving of raw sludge volume. The submerged combustion plant has consistently heated the sludge to 70°C with high efficiency of gas utilization before the anaerobic digestion stage. Some problems were experienced with the continuity of supply of the raw sludge but overall the plant has performed very satisfactorily with the production of a high quality disinfected and stabilized sludge for use by local farmers.     

Field evaluation of the treatability of type A zeolite in a trickling filter plant

Type A zeolite is a synthetic aluminosilicate which can be used as a builder in laundry detergents. The treatability of this zeolite in wastewater was evaluated in a trickling filter plant under field conditions. The normal performance of the plant was established during a baseline period of three months, after which the zeolite was added to the raw wastewater for 7 months. The removal of the zeolite by the plant averaged 81% or more at an influent concentration of 10 mg 1⁻¹. Of the zeolite that passed into the secondary effluent, 92% was removed by a dual-media filter. Removal from raw influent to tertiary effluent was thus 99%. The presence of the zeolite in the wastewater had no effect on the performance of the plant, the production of gas by the anaerobic digester or the concentrations of Pb, Zn and Ni in the effluent.     

Membrane regeneration for wastewater reclamation using reverse osmosis

One of the major problems in applying reverse osmosis to wastewater reclamation is the potential plugging and simultaneous product flux-decline of the membranes. At present two techniques are prevalently used to minimize these deleterious effects. These are periodic clearing and extensive pretreatment. A third, and as yet untried, technique is presented here. It involves the in situ replacement of degraded membranes at projected replacement costs far below those for spirally wound units.Results presented here demonstrate that in situ replacement of cellulose acetate reverse osmosis membranes is technically sound. The membrane replacement cycle was repeated six times with average water fluxes of about 13 gal ft⁻² day⁻¹ and salt rejections of between 78 and 85 per cent. The regenerable unit was also tested on primary and secondary sewage effluent. Average water fluxes were between 3 and 10 gal ft⁻² day⁻¹, respectively, while salt rejections were between 66 and 73 per cent. Projected membrane costs are reduced from $4.06 ft⁻² for a 6-in. dia. module to $0.08 ft⁻² for a 72-in. dia. module. Thus, large diameter units become economically very attractive. Design and cost computer parametrization is also presented.     

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.     

两相一体式污泥浓缩消化反应器的性能研究

在中温条件下,对两相一体式污泥浓缩消化反应器(TISTD)处理污泥的性能进行了深入的研究.当投配率为30%、进泥含水率为99.2%～99.8%、VS/TS为0.55～0.61时,排泥的含水率为93.5%～95.5%,VS/TS为0.33～0.40,产气量为18～24.5 L/d.经TISTD处理后,污泥的脱氢酶活性大大降低;18.6%～32.6%的总氮进入到上清液中,64.6%～81.0%的总氮在排出的厌氧污泥中;23.5%～28.3%的总磷进入到上清液中,70.7%～75.1%的总磷在排出的厌氧污泥中.     

Monitoring the role of aceticlasts in anaerobic digestion: activity and capacity

Aceticlastic methanogens are seen as a key to digester capacity and stability. This paper develops and applies an assay to measure digester stability by measuring the maximum aceticlastic methane production rate (V_max,ac). The V_max,ac in combination with acetate concentrations was found to be an effective digestion monitoring tool to indicate process upsets. At steady state, thermophilic, first stage and short SRT digesters generally had a greater V_max,ac than mesophilic, second stage or long SRT digesters. The ratio of the V_max,ac to the plant aceticlastic methane production rate, termed the Acetate Capacity Number (ACN), is a measure of the excess capacity of the digester. Either V_max,ac or ACN can be used to estimate the capability to handle higher organic loading rates. Monod modeling was used to predict V_max,ac, ACN and maximum VS loading rates for mesophilic and thermophilic digestion and for staged digesters to better understand expected digestion capacity and stability.     

The anaerobic degradation of detergent range fatty alcohol ethoxylates. Studies with C-labelled model surfactants

The anaerobic degradation of fatty alcohol polyglycol ethers was studied in a model sludge digester employing stearyl alcohol ethoxylate which was ¹⁴C-labelled either in the alkyl or in the heptaglycol chain. After 4-weeks' incubation of the ¹⁴C-compounds at 35°C in the presence of raw sludge as additional digestible substrate more than 80% of the initial radioactivity was found as methane and carbon dioxide. In addition, the major part of radioactivity in the digested sludge, corresponding to nearly 10% of added ¹⁴C, was attributable to biomass so that ultimate degradation of the two model surfactants amounted to more than 90%. Analysis of the small fraction of radiolabelled metabolites in the sludge supernatant allowed conclusions with regard to the anaerobic degradation route of linear alcohol ethoxylates. After primary biodegradation of the surfactant molecule by scission into the alkyl and poly(ethylene glycol) moieties the further biodegradation of the latter seems to proceed as under aerobic conditions, i.e. via oxidative or hydrolytic depolymerization steps. Eventually, ultimate biodegradation of the obtained monomers (C₂-units) leads to the formation of the gaseous end products.     

Fossil organic carbon in wastewater and its fate in treatment plants

This study reports the presence of fossil organic carbon in wastewater and its fate in wastewater treatment plants. The findings pinpoint the inaccuracy of current greenhouse gas accounting guidelines which defines all organic carbon in wastewater to be of biogenic origin. Stable and radiocarbon isotopes (¹³C and ¹⁴C) were measured throughout the process train in four municipal wastewater treatment plants equipped with secondary activated sludge treatment. Isotopic mass balance analyses indicate that 4–14% of influent total organic carbon (TOC) is of fossil origin with concentrations between 6 and 35 mg/L; 88–98% of this is removed from the wastewater. The TOC mass balance analysis suggests that 39–65% of the fossil organic carbon from the influent is incorporated into the activated sludge through adsorption or from cell assimilation while 29–50% is likely transformed to carbon dioxide (CO₂) during secondary treatment. The fossil organic carbon fraction in the sludge undergoes further biodegradation during anaerobic digestion with a 12% decrease in mass. 1.4–6.3% of the influent TOC consists of both biogenic and fossil carbon is estimated to be emitted as fossil CO₂ from activated sludge treatment alone. The results suggest that current greenhouse gas accounting guidelines, which assume that all CO₂ emission from wastewater is biogenic may lead to underestimation of emissions.     

The anaerobic degradation of detergent range fatty alcohol ethoxylates. Studies with 14C-labelled model surfactants

The anaerobic degradation of fatty alcohol polyglycol ethers was studied in a model sludge digester employing stearyl alcohol ethoxylate which was ¹⁴C-labelled either in the alkyl or in the heptaglycol chain. After 4-weeks' incubation of the ¹⁴C-compounds at 35°C in the presence of raw sludge as additional digestible substrate more than 80% of the initial radioactivity was found as methane and carbon dioxide. In addition, the major part of radioactivity in the digested sludge, corresponding to nearly 10% of added ¹⁴C, was attributable to biomass so that ultimate degradation of the two model surfactants amounted to more than 90%. Analysis of the small fraction of radiolabelled metabolites in the sludge supernatant allowed conclusions with regard to the anaerobic degradation route of linear alcohol ethoxylates. After primary biodegradation of the surfactant molecule by scission into the alkyl and poly(ethylene glycol) moieties the further biodegradation of the latter seems to proceed as under aerobic conditions, i.e. via oxidative or hydrolytic depolymerization steps. Eventually, ultimate biodegradation of the obtained monomers (C₂-units) leads to the formation of the gaseous end products.     

Quantitative analysis of methanogenic community dynamics in three anaerobic batch digesters treating different wastewaters

Quantitative changes in methanogenic community structures, associated with performance data, were investigated in three anaerobic batch digesters treating synthetic glucose medium, whey permeate, and liquefied sewage sludge. All digesters were initially seeded with anaerobic sludge obtained from a local municipal wastewater treatment plant. Dynamics of methanogenic populations were monitored, at order and family levels, using real-time PCR based on the 16S rRNA gene. The molecular monitoring revealed that, in each digester, the quantitative structure of methanogenic community varied continuously over treatment time and the variation corresponded well to the changes in chemical profiles. Biphasic production of methane, associated with successive increases in aceticlastic (mainly Methanosarcinaceae) and hydrogenotrophic (mainly Methanomicrobiales) methanogenic groups, was observed in each digester. This corresponded to the diauxic utilization of acetate and longer-chain volatile fatty acids (C₃-C₆), mainly propionate. Additionally, the non-metric multidimensional scaling (NMDS) analysis of the quantification results demonstrated that the community shift patterns in three digesters were totally different from each other. Considering that the operating conditions in all trials were identical except substrates, the differences in quantitative shift profiles were suggested to be due to the different substrate compositions. This implied that the composition of wastewater could affect the evolution of quantitative methanogenic community structure in an anaerobic process. Overall, our results suggested that more attention to quantitative as well as qualitative approaches on microbial communities is needed for fundamental understanding of anaerobic processes, particularly under dynamic or transitional conditions.     

Anaerobic digestion of seven different sewage sludges: A biodegradability and modelling study

Seven mixed sewage sludges from different wastewater treatment plants, which have an anaerobic digester in operation, were evaluated in order to clarify the literature uncertainty with regard to the sewage sludge characterisation and biodegradability. Moreover, a methodology is provided to determine the Anaerobic Digestion Model No. 1 parameters, coefficients and initial state variables as well as a discussion about the accuracy of the first order solubilisation constant, which was obtained through biomethane potential test. The results of the biomethane potential tests showed ultimate methane potentials from 188 to 214 mL CH₄ g⁻¹ COD_fed, COD removals between 58 and 65% and two homogeneous groups for the first order solubilisation constant: (i) the lowest rate group from 0.23 to 0.35 day⁻¹ and (ii) the highest rate group from 0.27 to 0.43 day⁻¹. However, no statistically significant relationship between the ultimate methane potential or the disintegration constant and the sewage sludge characterisation was found. Next, a methodology based on the sludge characterisation before and after the biomethane potential test was developed to calculate the biodegradable fraction, the composite concentration and stoichiometric coefficients and the soluble COD of the sewage sludge; required parameters for the implementation of the Anaerobic Digestion Model No. 1. The comparison of the experimental and the simulation results proved the consistency of the developed methodology. Nevertheless, an underestimation of the first order solubilisation constant was detected when the experimental results were simulated with the solubilisation constant obtained from the linear regression experimental data fitting. The latter phenomenon could be related to the accumulation of intermediary compounds during the biomethane potential assay.     

Mesophilic and thermophilic anaerobic digestion of faecal sludge in a pilot plant digester

In many developing countries, the sewage consisting of faecal sludge is discharged untreated into rivers, lakes and coastal areas. This poses a health hazard and a risk to the ecosystem, and wastes a resource which could produce sustainable energy. This paper reports results from an anaerobic digester of 1000L used for digestion of faecal waste at mesophilic and thermophilic conditions. The specific biogas production rate from faecal sludge was in the range of 0.06–0.12 m³/(kg DM.d) at mesophilic conditions at NTP (Normal Temperature & Pressure i.e. 25 °C and 1 atm. Pressure) and 0.1–0.21 m³/(kg DM.d) at thermophilic conditions calculated at NTP. The number of toilet users affects the biogas production with changes in the organic loading rate. The results showed 97% reductionin chemical oxygen demand and 90% reduction in biological oxygen demand of anaerobic digester discharge water as compared to inlet substrate values.     

Performance of aerobic digestion at different sludge solid levels and operation patterns

Laboratory batch and semi-continuous experiments were carried out at 20°C on the aerobic digestion of primary sludges and waste secondary activated sludges. Solids concentrations up to 60.000 mg l⁻¹ (6%) for primary sludges and 20.000 mg l⁻¹ (2%) for waste secondary activated sludges, were employed. It was found that aerobic digestion of more concentrated sludges was associated with slower solids degradation rates, but in the studied range of concentrations, more concentrated sludges yielded a higher mass of volatile suspended solids decomposed per unit digester volume per day. For the primary and secondary sludges with the same volatile suspended solids concentration, the amounts of volatile suspended solids decomposed per unit digester volume per day were closely comparable.The results from batch digestion experiments proved not to be directly applicable to the design of continuous flow aerobic digesters. It was also demonstrated that the treatment of a sludge with a higher solids concentration could be an effective means of utilizing the digester volume while obtaining a reasonably well stabilized product sludge.