Anaerobic Sewage Treatment Research Articles

Harvesting Microalgal Biomass grown in Anaerobic Sewage Treatment Effluent by the Coagulation-Flocculation Method: Effect of pH

Harvesting is a critical step in microalgal biomass production process for many reasons. Among the existing techniques available for harvesting and dewatering microalgal biomass, recovery from aqueous medium by coagulation-flocculation has been the most economically viable process, althoughit is highly dependent on pH. This study aims to assess alternative coagulants compared to the standard coagulant aluminum sulfate for microalgal biomass recovery from anaerobic effluent of domestic sewage treatment. The effluent quality was also analyzed after biomass recovery. Coagulants represented by modified tannin, cationic starch and aluminum sulfate recovered more than 90% of algae biomass, at concentrations greater than 80 mg/L, in the pH range 7-10. Cationic starch promoted higher microalgal biomass recovery with a wider pH range. Powdered seeds of Moringa oleifera and Hibiscus esculentus(okra) gum promoted biomass removal of 50%, only in the acidic range of pH. After sedimentation of the microalgal biomass, the effluents showed a removal of >80% for phosphorus and nitrogen values and >50% for BOD and COD when using aluminum sulfate, cationic starch and modified tannin as coagulants. Natural organic coagulants in a wide pH range can replace aluminum sulfate, a reference coagulant in microalgal biomass recovery, without decreasing microalgal biomass harvesting efficiency and the quality of the final effluent.

Modeling the performance of sustainable sanitation systems using building information modeling

Having a reliable sanitation system is one of the aims of both developed and developing countries. This goal cannot be reached effectively without handling it in a sustainable manner. Considering the fact that Egypt is the highest water consumer and sewage producer in the region makes it even more challenging to work on this quest. The main problem which faces the sanitation municipalities in Egypt is that most of the sanitation infrastructure is aging because it was built in the first half of the previous century. This research aims at presenting a framework for planning sustainable sanitation collection and treatment systems through the utilization of Building Information Modeling (BIM), Building Performance Modeling (BPM) and Computer Simulation (CS). Firstly, the procedure of using BIM and the difference between BIM workflow and drafting-centric workflow are demonstrated to ensure clear understanding of the new system, Building Performance Modeling is utilized to model an anaerobic sewage treatment plant, and then the outputs of the model are presented. Information models of a part of a sewer network and an anaerobic treatment plant are introduced to show how Building Information Modeling can improve the sustainability of the system. Also, a simulation tool is presented to model the flow in the sewer network to help in monitoring the pipeline's performance, and condition. In addition, it aids in detecting any failures in the system and in guiding the operator to the most suitable rehabilitation or replacement technique to deal with the detected failure. Finally, a solar study is introduced to replace the auxiliary electrical loads of the buildings in the wastewater treatment plant with solar energy to enforce the environmental and economical dimensions of sustainability.

The use of novel packing material for improving methane oxidation in biofilters

The use of biofilters (working bed volume of 7.85 L) for the oxidation of CH4 at low concentrations (from 0.17%v/v to 3.63%v/v, typically in waste gas from anaerobic sewage treatment) was investigated and four empty bed residence times were tested (in min): 42.8, 29.5, 19.6, and 7.4. Mixtures of organic (composted leaves) and three non-organic materials (sponge-based material - SBM, blast furnace slag - BFS, and expanded vermiculite - ExpV) were used as packing media. Along 188 operational days after the steady state was reached (95 days for start-up), the CH4 mineralization decreased while the inlet loads gradually increased from 3.0 ± 0.8 gCH4 m−3 h−1 to 148.8 ± 4.4 gCH4 m−3 h−1. The biofilter packed with ExpV showed the best results, since the CH4 conversions decreased from 95.0 ± 5.0% to 12.7 ± 3.7% as a function of inlet concentration, compared to the other two biofilters (SBM and BFS) which showed CH4 conversions decreasing from 56.0 ± 5.4% to 3.5 ± 1.2% as a function of inlet concentration. The methanotrophic activity of biomass taken from ExpV biofilter was three times higher than the activity of biomass from the other two biofilters. Taken together, these results suggested that ExpV provides an attractive environment for microbial growth, besides the mechanical resistance provided to the whole packing media, showing the potential to its use in biofiltration of diffuse CH4 emissions.

Recovery of elemental sulphur from anaerobic effluents through the biological oxidation of sulphides

ABSTRACTThe aim of the present study was to evaluate the biological oxidation of sulphide in two different UASB reactors by assessing the occurrence of oxidized forms of sulphur in the effluents and the amount of S0 that could be recovered in the process. The bioreactors employed were an anaerobic hybrid (AH) reactor employing porous polyurethane foam as support media and a micro-aerated UASB reactor equipped with an aeration device above the digestion zone. The AH reactor produced a final effluent containing low concentrations of S2– (3.87% of total sulphur load). It was achieved due to a complete oxidation of 56.1% of total sulphur. The partial biological oxidation that occurred in the AH reactor allowed the recovery of 30% of the sulphur load as S0. The effluent from the micro-aerated UASB reactor contained 5% of the sulphur load in the form of S2–, while 20.9% was present as dissolved SO42– and 46% was precipitated as S0. It is concluded that the AH reactor or micro-aeration carried out above the digestion zone of the UASB reactor favoured the biological oxidation of S2– and the release of odourless effluents. Both technologies represent feasible and low-cost alternatives for the anaerobic treatment of domestic sewage.

Influence of phase separator design on the performance of UASB reactors treating municipal wastewater

The objective of anaerobic sewage treatment is to maximize the fraction of influent organic material that is transformed into methane, thus minimizing the COD fractions that are discharged with the effluent or in the excess sludge production. Experimental data in this paper show that in the case of application of a UASB reactor for sewage treatment, the phase separator design has an important influence on digestion efficiency. An efficient phase separator leads to retention of a larger sludge mass, which means that the mean solids retention time is increased. The data show that the mean solids retention time or sludge age is the fundamental operational parameter that determines the efficiency of the anaerobic treatment. A simple way to improve the phase separator performance is to apply parallel plates in the settling section of the UASB reactor, above the conventional phase separator design of triangular prisms with an open base.

Anaerobic sewage treatment: state of the art, constraints and challenges

The interest in high-rate anaerobic (pre-)treatment of sewage using UASB reactors is steadily growing since its introduction in the mid-1980s. Today there are hundreds of full-scale plants in operation in various parts of the tropical world, notably in Latin America and India. The main advantage of UASB technology is the very low or even zero energy demand, leading to an up to tenfold drop in operational costs compared to activated sludge. This paper presents a literature review focussing on current design criteria and post-treatment options, alongside discussing the centralized and decentralized approach. The current limitations and constraints regarding temperature, nutrients, pathogen removal, odour nuisance, operational constrictions and methane emissions are also presented and discussed. Further, recent challenges in relation to energy recovery from biogas, sludge and scum are discussed, alongside with advances related to recovery of dissolved methane and sludge management. Finally, the paper provides some outlooks for upcoming developments.

Nitrogen and phosphorus removal in an anaerobic (UASB)-aerobic (ABF) sewage treatment system

Anaerobic sewage treatment process using upflow anaerobic sludge blanket (UASB) coupled with aerated biofilter (ABF) was tested for the removal of nitrogen and phosphorus by recycling the final effluent and by adding alum to the influent. TCOD Removal efficiency was about 60% in UASB without recycling of the ABF effluent, while it increased to 90% at recycling ratio of 3. Complete denitrification had occurred in the UASB, and removal efficiencies of both total nitrogen (TN) and NH4+-N were also improved to 74 and 96%, respectively, by recycling the nitrified ABF effluent. Total phosphorus (TP) removal was not improved by recycling of the ABF effluent. TP and soluble phosphorus were effectively removed in UASB by adding alum to the influent. 90% removal of TP was possible with alum dose at Al/P mole ratio of 2.6. In the final effluent, concentrations of TCOD, TN, and TP were below 14.0, 7.0, and 0.27 mg/L, respectively, in the UASB-ABF sewage treatment system at recycling ratio of 3 with alum.

Anaerobic treatment of domestic sewage in modified septic tanks at low temperature

Three laboratory-scale septic tanks, an anaerobic baffled reactor (ABR)-septic tank (R1), a Yuhuan drawing three-dimensional-carrier-septic tank (R2) and a conventional septic tank (R3), were operated in parallel over half a year under hydraulic retention times (HRTs) of 36, 24 and 12 h, with a sewage temperature of 16°C. The removal efficiencies of total chemical oxygen demand (CODtot) achieved in R1 and R2 increased by 14%, 21% and 12% and 18%, 3% and 16%, respectively, under three different HRTs, as compared to those in R3. The total nitrogen and phosphorus removal efficiencies were negligible. R1 sludges had a higher specific methane production rate as compared to that of R2 and R3 sludges. The results indicated that the two modified septic tanks can improve the performance in terms of COD and total solids removal, both were suitable technologies for domestic sewage (pre) treatment at low temperature in northern China.

Effects of organic carbon source, chemical oxygen demand/N ratio and temperature on autotrophic nitrogen removal.

To assess the feasibility of the Anammox process as a cost-effective post-treatment step for anaerobic sewage treatment, the simultaneous effects of organic carbon source, chemical oxygen demand (COD)/N ratio, and temperature on autotrophic nitrogen removal was studied. In batch experiments, three operating conditions were evaluated at 14, 22 and 30 °C, and at COD/N ratios of 2 and 6. For each operating condition, containing 32 ± 2 mg NH4(+)-N/L and 25 ± 2 mg NO2(-)-N/L, three different substrate combinations were tested to simulate the presence of readily biodegradable and slowly biodegradable organic matter (RBCOD and SBCOD, respectively): (i) acetate (RBCOD); (ii) starch (SBCOD); and (iii) acetate + starch. The observed stoichiometric NO2(-)-N/NH4(+)-N conversion ratios were in the range of 1.19-1.43, and the single or simultaneous presence of acetate and starch did not affect the Anammox metabolism. High Anammox nitrogen removal was observed at 22 °C (77-84%) and 30 °C (73-79%), whereas there was no nitrogen removal at 14 °C; the Anammox activity was strongly influenced by temperature, in spite of the COD source and COD/N ratios applied. These results suggest that the Anammox process could be applied as a nitrogen removal post-treatment for anaerobic sewage systems in warm climates.

Co-digestion to support low temperature anaerobic pretreatment of municipal sewage in a UASB–digester

The aim of this work was to demonstrate that co-digestion improves soluble sewage COD removal efficiency in treatment of low temperature municipal sewage by a UASB-digester system. A pilot scale UASB-digester system was applied to treat real municipal sewage, and glucose was chosen as a model co-substrate. Co-substrate was added in the sludge digester to produce additional methanogenic biomass, which was continuously recycled to inoculate the UASB reactor. Soluble sewage COD removal efficiency increased from 6 to 23%, which was similar to its biological methane potential (BMP). Specific methanogenic activity of the UASB and of the digester sludge at 15°C tripled to a value respectively of 43 and 39 mg CH4-COD/(g VSS d). Methane production in the UASB reactor increased by more than 90% due to its doubled methanogenic capacity. Therefore, co-digestion is a suitable approach to support a UASB-digester for pretreatment of low temperature municipal sewage.

UASB를 이용한 혐기성 하수처리공정에서 ABF 유출수 반송에 따른 유기물질과 질소 및 인 제거

Nitrogen and phosphorus removal was investigated in an UASB-ABF (Up-flow anaerobic sludge blanket aerated biofilter) anaerobic sewage treatment system. Successful removal of nitrogen and phosphorus with organic matters was possible in the UASB-ABF system from the results of 160 days operation with the influent raw domestic sewage. Removal efficiencies of organic matter (as TCOD) showed 64% in UASB without recycle of the ABF effluent, however, they increased to 92%, 95%, 96% with 120%, 180% and 240% recycle of the ABF effluent, respectively. Increasement of the organic matter removal was not prominent at recycle ratio above 180%. Apparent increase in TN removal occurred with recycle of the ABF effluent. TN removal efficiency was 18% without recycle, but it increased to 82% with 240% recycle of the ABF effluent. And stable nitrification above 95% was possible as a result of efficient removal of organic matter in the UASB with and without recycle of the effluent. Removal of both TP and PO4-P also increased remarkably with recycle of the effluent. Without recycle of the effluent, that is at strict anaerobic condition in UASB, TP was not removed, however, its removal efficiency increased to 51%, 63%, 71% at recycle ratios of 120%, 180%, 240%, respectively mainly at UASB.

The effect of sludge recirculation rate on a UASB-digester treating domestic sewage at 15 °C

The anaerobic treatment of low strength domestic sewage at low temperature is an attractive and important topic at present. The upflow anaerobic sludge bed (UASB)-digester system is one of the anaerobic systems to challenge low temperature and concentrations. The effect of sludge recirculation rate on a UASB-digester system treating domestic sewage at 15 °C was studied in this research. A sludge recirculation rate of 0.9, 2.6 and 12.5% of the influent flow rate was investigated. The results showed that the total chemical oxygen demand (COD) removal efficiency rose with increasing sludge recirculation rate. A sludge recirculation rate of 0.9% of the influent flow rate led to organic solids accumulation in the UASB reactor. After the sludge recirculation rate increased from 0.9 to 2.6%, the stability of the UASB sludge was substantially improved from 0.37 to 0.15 g CH₄-COD/g COD, and the bio-gas production in the digester went up from 2.9 to 7.4 L/d. The stability of the UASB sludge and bio-gas production in the digester were not significantly further improved by increasing sludge recirculation rate to 12.5% of the influent flow rate, but the biogas production in the UASB increased from 0.37 to 1.2 L/d. It is recommended to apply a maximum sludge recirculation rate of 2-2.5% of the influent flow rate in a UASB-digester system, as this still allows energy self-sufficiency of the system.

Enrichment of denitrifying methanotrophic bacteria for application after direct low-temperature anaerobic sewage treatment

Despite many advantages of anaerobic sewage treatment over conventional activated sludge treatment, it has not yet been applied in temperate zones. This is especially because effluent from low-temperature anaerobic treatment contains nitrogen and dissolved methane. The presence of nitrogen and methane offers the opportunity to develop a reactor in which methane is used as electron donor for denitrification. Such a reactor could be used in a new concept for low-temperature anaerobic sewage treatment, consisting of a UASB-digester system, a reactor for denitrification coupled to anaerobic methane oxidation, and a nitritation reactor. In the present study denitrifying methanotrophic bacteria similar to ‘Candidatus Methylomirabilis oxyfera’ were enriched. Maximum volumetric nitrite consumption rates were 33.5mgNO2−-N/Ld (using synthetic medium) and 37.8mgNO2−-N/Ld (using medium containing effluent from a sewage treatment plant), which are similar to the maximum rate reported so far. Though the goal was to increase the rates, in both reactors, after reaching these maximum rates, volumetric nitrite consumption rates decreased in time. Results indicate biomass washout may have significantly decelerated enrichment. Therefore, to obtain higher volumetric consumption rates, further research should focus on systems with complete biomass retention.

Mathematical Simulation Study on Performance of Different Opposite Folded Plate Anaerobic Sewage Treatment Technology

The effect of different hydraulic retention time on the removal of COD, nitrogen and phosphorous when influent COD was 1000 mg/L were carried out by establishing simulation model with the help of mathematical simulation software BioWin3.0 on the computer and adjusting the parameters continuously combined with the actual operation of anaerobic sewage treatment technology, then compared and analyzed the effect of the simulated effluent and the actual effluent. The results showed that the model established by mathematical simulation software BioWin3.0 can reflect the actual operation conditions of sewage treatment.

유동상 반응조를 이용한 하수의 혐기성 처리에 관한 연구

Anaerobic sewage treatment is drawing attentions due to high energy consumptions and sludge production associated with aerobic treatment. This study evaluates the treatment characteristics and energy balance of a fluidized bed reactor (FBR) for treating domestic sewage at <TEX>$20^{\circ}C{\sim}25^{\circ}C$</TEX> for 245 days. Sewage fed to the FBR was a primary clarifier effluent of a domestic sewage treatment plant with COD of 99-301 mg/L and <TEX>$BOD_{5}$</TEX> of 37-149 mg/L. Effluent <TEX>$SBOD_{5}$</TEX> and its removal efficiency at HRT of 1~3 h were 6~15 mg/L and 73.4~85.5%, respectively, achieving high removal efficiency for soluble organic substances even at short HRTs. COD removal efficiency and its effluent concentration were 53.8~75.9% and 51~83 mg/L, respectively. The energy production potential from gaseous methane was 0.009-0.028 kWh/<TEX>$m^{3}$</TEX>, which satisfies the energy required for the FBR operation.

Design investigation of a solar energy heating system for anaerobic sewage treatment

Domestic and international researches of solar energy heating for anaerobic wastewater treatment are described in this paper. The design investigation of a solar heating anaerobic sewage treatment system for cold regions is proposed, (I) developing of a solar water heating system for treatment, (II) developing of a high-rate anaerobic reactor for sewage treatment under normal temperature conditions, and (III) solving problems of joint control between the solar water heating system and the anaerobic reactor. This article provides a reference for design and application of the solar energy heating system for anaerobic sewage treatment.

A tribute to Thomas Roosevelt Punnett, Jr. (1926–2008)

We honor here Thomas (Tom) Roosevelt Punnett, Jr. (May 25, 1926-July 4, 2008), who was a pioneer of Biology, particularly of biochemistry of plants and algae, having specialized in photosynthesis under Robert Emerson of the University of Illinois at Urbana-Champaign. He did exciting work on regulation and control of various metabolic reactions. He was an innovator and raconteur par excellence, and he prized critical thinking. His enthusiasm for basic science questions was matched by his grasp of their "real-world" implications. His last project was a patent for anaerobic sewage treatment that he hoped would lead to solution of waste disposal and energy creation world wide, including the clean-up of Lake Erie, where he had sailed as a boy. On the personal side, he had a strong sense of morality and a great wit and humor.

Fate of organic carbon in UAFB treating raw sewage: Impact of moderate to low temperature

The anaerobic biological treatment of raw sewage under low ambient temperatures was investigated in an up-flow anaerobic fixed bed (UAFB) reactor, over a 220-day trial period. The operating temperature was lowered stepwisely from 35 to 25, 20 and 15°C. Obvious accumulation of acetic acid was observed in the effluent as the temperature dropped, which almost tripled at 15°C compared to that at 35°C. An interesting psychrophilic-forward-shift trend of methane production rate following the decrease of temperature was discovered. The methane yield at each trial was 169, 201, 256 and 269 L(STP) CH(4)/kg COD(removed). For each temperature trial, about 32.6%, 28.3%, 34.4% and 34.9% were removed in form of methane. Based on PCR-DGGE results, the band corresponded to Methanosphaera spp. only showed up on 15°C profile. Analysis of both methane production and DGGE results indicated that psychro-tolerant microorganisms dominated the archaeal populations in the UAFB under low-temperature.

High-rate anaerobic treatment of domestic wastewater at ambient operating temperatures: A review on benefits and drawbacks

This paper reviews the current knowledge on high-rate anaerobic sewage treatment at ambient operating temperatures while presenting the benefits and drawbacks. Since domestic sewage is reported as the main point-source pollutant on a global scale, its treatment deserves ample research. In most of the cities and towns of some developing countries, wastewater produced in households is still discharged into the nearest water body without subjected any treatment. Therefore, simple, affordable, and effective sewage treatment systems are required. Anaerobic digestion of wastewater is reported as a sustainable alternative as recovery of energy is provided while nutrients are preserved for reuse. Anaerobic sewage treatment is certainly not limited to regions of hot climates but it also offers treatment potential in sub-tropical and even in moderate climatic regions due to their favorable temperature conditions. Since many sewage-like dilute wastewaters are discharged at low ambient temperatures especially under moderate climate conditions (15 to 20°C), heating the wastewater to maintain mesophilic conditions (35°C) for anaerobic treatment necessitates high energy and certainly high operating costs. Thus, the development of anaerobic treatment systems operated at ambient temperatures without doubt will have a great ecological and economic impact. High-rate anaerobic treatment systems, especially upflow anaerobic sludge blanket (UASB) reactors, have been occupying a noticeable position for sewage treatment in several tropical countries where artificial heating can be eliminated. However, in spite of their undeniable advantages, there are certain drawbacks of anaerobic sewage treatment at low operating temperatures which should be clarified. Among them, the main concern for anaerobic treatment application is its producing effluents that barely comply with the standarts for reuse in agriculture or discharge to the environment. Therefore, the effluents from anaerobic reactors usually necessitate a post-treatment step as a mean to protect the receiving water bodies. However, anaerobic sewage treatment when combined with a proper post-treatment, provides a sustainable, appropriate, and affordable method especially for developing countries.

Removal Capacity of Caffeine, Hormones, and Bisphenol by Aerobic and Anaerobic Sewage Treatment

The number of chemical compounds in sewage and consequently their release into the environment is increasing. Some of them are toxic and many of them are considered endocrine disrupters. Here, the capacity of three wastewater treatment plants (WWTPs) to remove caffeine, hormones and bisphenol-A was investigated. Bisphenol-A and caffeine are highly water-soluble compounds, as opposed to hormones (estradiol, estriol, and ethynilestradiol) which are hydrophobic compounds. In the Sewage Treatment Plant (SWT)1 the sewage is treated by activated sludge process, in the second plant, SWT2, sewage is treated by upflow anaerobic sludge blanket reactors followed by dissolved air flotation, and in the third, SWT3 sewage is treated by stabilization lagoons. The first lagoon is 3.5 m deep, thus facultative and polishment processes occur. It was speculated that there was a difference in efficiency between the three plants in removing micropollutants. Small differences were found in the amounts removed, probably accounted for by retention time. The caffeine and bisphenol-A were almost completely removed, higher than 90% for both compounds (bisphenol-A and caffeine) in all WWTPs. The hormones, however, had a smaller rate of removal, between 70% and 87%. It is suspected that retention time is essential for removal efficiency, together with type of treatment. In fact, the hormones, caffeine, and bisphenol-A found in the environment definitely come from untreated sewage.