Upflow Anaerobic Sludge Blanket Reactor Research Articles

Recent Developments in Biological Processing Technology for Palm Oil Mill Effluent Treatment-A Review.

Simple SummaryPalm oil mill effluent (POME) requires treatment prior to discharge to the environment. Biological processing technology is highly preferable due to its advantages of environmentally friendliness, cost effectiveness, and practicality. These methods utilized various designs and modifications of bioreactors fostering effective fermentation technology in the presence of fungi, bacteria, microalgae, and a consortium of microorganisms. This review highlights the recent biological processing technology for POME treatment as a resource utilization.POME is the most voluminous waste generated from palm oil milling activities. The discharge of POME into the environment without any treatment processing could inflict an undesirable hazard to humans and the environment due to its high amount of toxins, organic, and inorganic materials. The treatment of POME prior to discharge into the environment is utmost required to protect the liability for human health and the environment. Biological treatments are preferable due to eco-friendly attributes that are technically and economically feasible. The goal of this review article is to highlight the current state of development in the biological processing technologies for POME treatment. These biological processing technologies are conducted in the presence of fungi, bacteria, microalgae, and a consortium of microorganisms. Numerous microbes are listed to identify the most efficient strain by monitoring the BOD, COD, working volume of the reactor, and treatment time. The most effective processing technology for POME treatment uses an upflow anaerobic sludge blanket reactor with the COD value of 99%, hydraulic retention time of 7.2 days, and a working volume of 4.7 litres. Biological processing technologies are mooted as an efficient and sustainable management practice of POME waste.

Single step production of activated carbon from microalgae cultivated with urban wastewater

The production of activated carbon using as precursor a microalgae biomass produced in a wastewater treatment plant, consisting of an Upflow Anaerobic Sludge Blanket (UASB) reactor, followed by high-rate aerobic ponds, was studied. The harvest of microalgae biomass was carried out through coagulation with Tanfloc®, flocculation and settling. Activated carbon (AC) production was tested at 650 °C and 800 °C, with carbonization and activation performed in a single step, by the physical method with water vapor in different proportions of water mass relative to the sample mass. The specific surface area ranged from 10 to 177 m2·g−1 in samples produced at 650 °C and from 602 to 630 m2·g−1 in the ones produced at 800 °C. It is concluded that the harvested microalgae biomass can be used as a precursor of activated carbon. The best condition tested for the production of AC was carbonization at 800 °C and activation with water vapor in the ratio of 4 gwater/gsample. The results prove that the process of carbonization and physical activation can be done with water vapor in a single step and that activated carbons obtained under the highest temperature (>800 °C) are predominantly micro and mesoporous, with a predominantly aromatic structure.

Assessment of Levonorgestrel Leaching in a Landfill and Its Effects on Placental Cell Lines and Sperm Cells

The Buenavista landfill is located east of the city of Medellín, but it has a slope steeper than 30% and is less than 600 m away from the Piedras River, possibly influencing the quality of the drinking water in the city. Many complex residues are disposed of in this landfill, including pharmaceuticals and personal care products (PPCPs) such as levonorgestrel (LNG), which may reach water bodies via runoff and leaching. We assessed the levels of LNG in the effluent of an upflow anaerobic sludge blanket (UASB) reactor from the Buenavista landfill by uHPLC–DAD, as well as the endocrine disruptor effect of LNG on placental cell lines (BeWo) and human sperm cells. Additionally, the potential leaching of LNG was assayed under laboratory conditions using soil layers that were sampled from the Buenavista landfill. LNG was detected at levels of 315 μg·L−1 in the effluents of the UASB reactor. Thus, the UASB reactor is not an efficient treatment method for the removal of recalcitrant pollutants. Additionally, we found that a layer of soil used as a cover material may adsorb more than 90% of LNG pollutants, but small amounts may still be leached, which means that a cover material is not a strong enough barrier to fully prevent the leaching of LNG. Finally, our results show that the leachate fraction decreased the levels of β-human chorionic gonadotropin, but not sperm motility or viability. Thus, leached LNG could trigger reproduction disorders, but further studies should be carried out to investigate its potential effects in more detail.

Effects of temperature and HRT on biogas production in moving and fixed bed of a novel upflow anaerobic hybrid (UAHB) reactor

ABSTRACT The upflow anaerobic hybrid (UAHB) reactor combines the advantages of a upflow anaerobic sludge blanket (UASB-type) reactor and an anaerobic filter in a single compartment. A novel configuration of the UAHB reactor, composed of two three-phase separators (3PHS), was proposed to evaluate the biogas production in the moving and fixed bed in the treatment of synthetic sewage at a temperature range of 14–21 °C and hydraulic retention time (HRT) of 12, 10 and 8 h. The bench-scale reactor was operated in three different phases with organic loading rate (VOLR) of 0.6 (0.3–0.7), 0.7 ± 0.2, and 1.1 ± 0.1 kg COD m−3 d−1, respectively, for 225 days. The average removal efficiency of chemical oxygen demand (CODt) was 78 (42–89)%, and the total biogas yield was 3090 (1704–4782) mL d−1, with 66% of the lower 3PHS (moving bed) and 34% of the upper 3PHS (fixed bed). However, no significant difference was observed between the biogas yield on the 3PHS (p-value = 0.5048), thus confirming the influence of temperature in the biogas production. The average percentage of methane was 76 (60–82)% for both beds, and the filter media increased the production by 21%. Thus, it can be concluded that the fixed bed suppressed the instability of the moving bed regarding the biogas production and contributed to the final quality of the effluent.

Psychrophilic treatment of municipal wastewater with a combined UASB/ASD system, and perspectives for improving urban WWTP sustainability

According to new paradigms of urban wastewater management, energy savings and resources and energy recovery from sewage will assume an ever-increasing importance. Anaerobic processes, aside from being more energy efficient than conventional aerobic ones, are particularly suited to recover embedded organic energy, improving the overall energy balance of treatment processes, however, their performance is limited by low temperatures and slower kinetics. In this study, a pilot Upflow Anaerobic Sludge Blanket (UASB) reactor was operated to treat municipal wastewater at low temperature regime (16.5–18.5 °C) for 22 weeks, both as standalone process and combined with a sidestream anaerobic sludge digester. Process performance highlighted good system robustness, as proved by stable pH and volatile fatty acid/total alkaline buffer capacity ratio, even though observed methane yield was low. Observed COD and TSS removal efficiencies were in the ranges of 60–69% and 63–73%, respectively. Methane production ranged between 0.106 and 0.132 Nm3CH4/kgCODrem. An economic assessment was carried out to evaluate the feasibility and benefits of implementing UASB pre-treatment of municipal wastewater in existing conventional facilities (activated sludge and anaerobic sludge digestion), showing that significant energy demand reduction could be achieved for both biological secondary treatment and sludge management, leading to considerable operational economies, and possible positive economic returns within a short pay-back period (3–4 yrs).

Phosphorus recovery from pig manure: Dissolution of struvite and formation of calcium phosphate granules during anaerobic digestion with calcium addition

Phosphorus is an essential but finite and scarce element, which is used extensively in pig farming. For recovering phosphorus from pig manure, we hypothesize that calcium addition during anaerobic treatment can trigger calcium phosphate granulation and enable efficient phosphorus recovery. In this study, we tested the recovery of phosphorus from pig manure by adding calcium during anaerobic treatment. Size–separated (<200 µm) pig manure was treated in two identical up-flow anaerobic sludge blanket reactors for 456 days. Calcium was supplied to one of the reactors to study calcium phosphate granulation.Calcium addition showed a positive effect on treatment stability and efficiency, increasing chemical oxygen demand and phosphorus removal. Phosphorus removal increased from 60% without calcium addition to 74% with calcium addition. The addition of calcium increased the phosphorus concentration in significantly larger particles, calcium phosphate granules, (79% >0.4 mm compared with 11% without calcium addition) in the reactor with calcium addition, which enables separation and a transport reduction of 85% for the recovered phosphorus. The main phosphorus phase in the reactor sludge bed changed from struvite to calcium phosphate with calcium addition. The Mg:P molar ratio was 0.09 with calcium addition and 0.88 without calcium addition in particles >2.5 mm. Thus, calcium addition enhances the treatment of pig manure and enables phosphate recovery as calcium phosphate granules.

Modified fractional-order model for biomass degradation in an up-flow anaerobic sludge blanket reactor at Zenein Wastewater Treatment Plant.

This paper presents a modified fractional-order model (FOM) for microorganism stimulation in an up-flow anaerobic sludge blanket (UASB) reactor treating low-strength wastewater. This study aimed to examine the famine period of methanogens due to biomass accumulation in the UASB reactor over long time periods at a constant organic loading rate (OLR). This modified model can investigate the substrate biodegradation in a UASB reactor while considering substrate diffusion into biological granules during the feast and famine periods of methanogens. The Grünwald-Letnikov numerical technique was used to indicate the effect of biomass degradation on the biogas production rate and substrate biodegradation in a UASB reactor installed at Zenein Wastewater Treatment Plant (WWTP) in Giza, Egypt. Several fractional orders were applied in the dynamic model at biomass concentrations of [Formula: see text] and [Formula: see text] in the reactor bed and blanket zones, respectively. An OLR of [Formula: see text] using the calibrated kinetic parameters at [Formula: see text] was applied to comply with the experimental outcomes. The simulation results indicate that the removal efficiency of chemical oxygen demand (COD) was maintained at approximately [Formula: see text], whereas the biogas production rate declined from [Formula: see text] in the reactor bed zone due to a decline in food to microorganism (F/M) ratio from [Formula: see text] during the sludge retention time (SRT) in the UASB reactor.

Performance of full-scale slaughterhouse effluent treatment plant (SETP)

This paper studied the effectiveness of a slaughterhouse wastewater treatment plant. The purpose of this study is to evaluate the slaughterhouse effluent treatment plant (SETP) in eliminating impurities, as well as the variables that affect performance. The SETP consisted of a dissolved air floatation (DAF) system with an up-flow anaerobic sludge blanket (UASB) reactor followed by two activated sludge processessing (ASP) stages. The removal efficiencies of chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS) were 74.7%, 76.8%, and 90.14%, respectively. The study proposes constructing a tertiary treatment facility, installing two dung squeezers, and commissioning the UASB.

Micropollutants removal during high rate thermophilic and hyper-thermophilic anaerobic digestion of concentrated black water

Source separated toilet water (black water; BW) is an important alternative nutrient source for agriculture. However, reuse and recovery of nutrients from BW is limited by the presence of pollutants, such as pathogens and micropollutants. In this study, the fate of micropollutants during thermophilic and hyper-thermophilic anaerobic digestion (AD) of concentrated vacuum collected BW is assessed. A total of eight pharmaceuticals were selected and spiked with two distinct loading rates to concentrated BW treated in an Upflow Anaerobic Sludge Blanket Reactors (UASB). The removal of these micropollutants was followed by measuring concentrations in the liquid phase. It was shown that the micropollutant loading rate did not affect the removal efficiency. Irbesartan, propanol, sulfamethoxazole and trimethoprim were almost completely removed under both conditions (>95% removal). Metoprolol had 74% removal under thermophilic conditions. Caffeine showed high desorption from BW solids, whereas carbamazepine is thought to be removed by sorption to the sludge in the UASB reactor. Diclofenac removal was < 30% during both temperature conditions, which may have been caused by the lack of sludge adaptation which limits the biodegradation. There were no differences in micropollutant removal efficiencies between thermophilic and hyper-thermophilic AD of concentrated BW. Therefore, it is concluded that thermophilic AD is sufficient for safe nutrient recovery in terms of micropollutants presence.

Development and performance of a dynamic membrane for anaerobic wastewater treatment - an analysis with different mesh pore sizes and configurations.

Recent studies have focused on proposing materials with larger pores and lower cost to replace conventional membranes. This study aims to investigate the performance of an anaerobic dynamic membrane bioreactor (AnDMBR) at pilot scale, acting as a post-treatment for an Upflow Anaerobic Sludge Blanket (UASB) reactor treating sewage, for the removal of complementary organic matter, focusing on the module design, dynamic layer formation and process performance. The configurations tested on this study were: UASB followed by stone filter and three AnDMBRs in series with polyester pore sizes of 100 μm, 50 μm, and 5 μm; UASB followed by disc filter and the three AnDMBRs in series; UASB followed by the three AnDMBRs in series; and UASB reactor with only one AnDMBR module. Regarding the studied configurations, high removals of total suspended solids, chemical oxygen demand, and turbidity were achieved in all experimental setups. The use of stone and disc filters did not bring clear benefits to the system concerning the direct application of filtration with dynamic membranes, therefore, their removal in the system was favorable. The dynamic membrane formation was faster in the 50 μm mesh, and only a few hours were necessary to obtain a permeate quality with a total suspended solids concentration and a turbidity lower than 15 mg·L-1 and 30 NTU, respectively. Thus, the dynamic membrane technology proved to be a potential solution in the post-treatment of UASB reactor effluents.

Performance of the UASB reactor during wastewater treatment and the effect of the biogas bubbles on its hydrodynamics

ABSTRACT A lab-scale Upflow Anaerobic Sludge Blanket (UASB) reactor was used as a model for evaluating synthetic and complex industrial wastewater treatment, using a solar heater to control temperature. Also, hydrodynamics was assessed using the Computational Fluid Dynamics (CFD) method. Initially, the UASB reactor was operated with synthetic wastewater at Hydraulic Retention Time (HRT) of 24 h in 20 ± 2 °C and 30 ± 2 °C to measure the biogas bubbles production for CFD study. COD removal efficiencies of 85 ± 3% and 95 ± 3%, respectively, with production of 27 and 39 ml CH4/h, correspondingly, were observed. After that, the reactor was fed with complex industrial wastewater. It was evaluated at 24 h in both temperatures. At 30 °C, low COD removal efficiency was observed, being 48 ± 13%, with methane production of 20 ± 3 ml CH4/h. The plug flow pattern was observed in the CFD modelling at HRT of 24 h and 20 °C without considering biogas bubbles interaction. Similar hydrodynamic behaviour was observed at HRT of 24 h and 30 °C. Nonetheless, when biogas bubbles were considered in the CFD modelling, hydrodynamics significantly changed, passing from a plug flow to a complete mix flow pattern.

Organic matter removal in a simultaneous nitrification–denitrification process using fixed-film system

Swine wastewater treatment is a complex challenge, due to the high organic matter (OM) and nitrogen (N) concentrations which require an efficient process. This study focused on evaluating two different support media for OM and N removal from an Upflow Anaerobic Sludge Blanket (UASB) reactor fed with swine wastewater. Maximum specific nitrification (MSNA) and denitrification (MSDA) activity test for both biofilm and suspended biomass were carried out using as supports: polyurethane foam (R1) and polyethylene rings (R2). The results showed that R2 system was more efficiently than R1, reaching OM removal of 77 ± 8% and N of 98 ± 4%, attributed to higher specific denitrifying activity recorded (5.3 ± 0.34 g NO3-N/g TVS∙h). Furthermore, 40 ± 5% of the initial N in the wastewater could have been transformed into molecular nitrogen through SND, of which only 10 ± 1% was volatilized. In this sense, MSDA tests indicated that suspended biomass was responsible for at least 70% of N removal and only 20% can be attributed to biofilm. SND could be confirmed with the analysis of microbial diversity, due to the presence of the genus Pseudomonas dominated the prokaryotic community of the system in 54.4%.

Simultaneous aerobic-anaerobic biodegradation of an industrial effluent of polymeric resins with high phenol concentration at different organic loading rates in a non-conventional UASB type reactor

The presence of phenol in the environment is a consequence of both natural actions and anthropogenic contributions, mainly of an agricultural and industrial nature. Its concentration in wastewater ranges from 0.1 to 3,900 mg/L and in some cases from 30,000 to 80,000 mg/L. Among the technologies used for its elimination, are the physicochemical, biological, adsorption, and chemical oxidation processes. For its recovery, there is adsorption, ion exchange, extraction, volatilization, polymerization, electrocoagulation, advanced oxidation and ion exchange. In this research, a new configuration Upflow Anaerobic Sludge Blanket reactor (UASB) was studied to biodegrade the phenol present in an industrial effluent of polymeric resins by varying the organic load rate in 3.2 ± 0.6, 13.9 ± 0.8, 33.5 ± 1.1 and 34.6 ± 0.9 kg COD/m3.d, at two rates of Dissolved Oxygen (DO): 0.78 ± 0.18 mg/L (experiments 1–3) and 1.23 ± 0.02 mg/L (experiment 4), with a Hydraulic Retention Time (HRT) of 0.5 days at 30 ± 0.5 °C. The results showed the best Chemical Oxygen Demand (COD) removal rate and phenol biodegradation (64 and 74%, respectively) at a lower organic load (experiment 1). With a gradual increase in this, during experiments 2 and 3, it decreased by 55.6 and 17%, respectively. However, by increasing the dissolved oxygen rate to 1.23 ± 0.02 mg/L during experiment 4, the phenol biodegradation rate was slightly improved, but not the COD removal rate.

Use of spray nozzles to recover dissolved methane from an Upflow Anaerobic Sludge Blanket (UASB) reactor effluent.

Methane is a powerful greenhouse gas and a source of energy. Recovering this gas means lower greenhouse gas emission and potential reduction of energetic costs. The lack of full-scale results, the use of different methodologies to detect dissolved methane (d-CH4) and the fact that no process to remove d-CH4 from anaerobic effluents is energetically or economically viable at full-scale urged a different approach to the problem. To avoid methodological interference and facilitate comparison of results the Standard Test Method number D8028-17 published by ASTM International can be used to determine d-CH4. The use of real anaerobic reactor effluent also helps results to be compared. In this study, 80 samples from a full-scale anaerobic reactor showed an average concentration of dissolved methane of 14.9 mg·L-1, meaning an emission of 229 kg of CO2 eq·h-1 and an average of 113.5 kW wasted. Using spray nozzles, an alternative to the methods being researched, the average methane recovery was 11.5 mg·L-1 of CH4, an efficiency of 81.6%, meaning 177 kg of CO2 eq·h-1 emissions avoided and 87.9 kW of recoverable energy.

Effect of applying potentials on anaerobic digestion of high salinity organic wastewater

High salinity organic wastewater (HSOW) contains both organic pollutants and high concentration of inorganic salts. If it is discharged into the environment without proper treatment, it will cause adverse consequences such as dehydration and death of aquatic organisms, and soil salinization. Bioelectrochemical systems (BESs) have been applied in various wastewater treatment processes. To assess the feasibility of using BESs to treat HSOW, the effect of applying potential on anaerobic digestion of HSOW was explored in an up-flow anaerobic sludge blanket (UASB) reactor poised at −0.6 V (vs. Ag/AgCl). When organic loading rate (OLR) was 2.16–2.88 kg chemical oxygen demand/(m3d) (kg COD/(m3d)), the applied potential had no significant effect on the UASB performance. After OLR was increased to 4.32 kg COD/(m3d), the applied potential decreased COD removal efficiency and methane production and resulted in VFAs accumulation. Mesotoga was enriched on the electrode when potential was applied, causing decrease in relative abundances of acetoclastic methanogens. The abundance of Methanothrix on the electrode in the reactor with applied potential was much lower than in the control reactor (10% vs 28.9%), which might lead to decrease in performance of the reactor due to the depressed direct interspecies electron transfer (DIET) and less formation of granular sludge. These results suggest that applying external potentials has negative effect on the anaerobic treatment of HSOW, and should be taken into consideration in real HSOW treatment projects.

Reduction and liquid-solid partitioning of SARS-CoV-2 and adenovirus throughout the different stages of a pilot-scale wastewater treatment plant

Investigating waterborne viruses is of great importance to minimizing risks to public health. Viruses tend to adsorb to sludge particles from wastewater processes by electrostatic and hydrophobic interactions between virus, aquatic matrix, and particle surface. Sludge is often re-used in agriculture; therefore, its evaluation is also of great interest to public health. In the present study, a pilot scale system treating real domestic wastewater from a large city in Brazil was used to evaluate the removal, the overall reduction, and liquid-solid partitioning of human adenovirus (HAdV), the novel coronavirus (SARS-CoV-2) and fecal indicators (F-specific coliphages and E. coli). The system consists of a high-rate algal pond (HRAP) post-treating the effluent of an upflow anaerobic sludge blanket (UASB) reactor. Samples were collected from the influent and effluent of each unit, as well as from the sludge of the UASB and from the microalgae biomass in the HRAP. Pathogens and indicators were quantified by quantitative polymerase chain reaction (qPCR) (for HAdV), qPCR with reverse transcription (RTqPCR) (for SARS-CoV-2), the double agar plaque assay (for coliphages), and the most probable number (MPN) method (for E. coli). The removal and overall reduction of HAdV and SARS-CoV-2 was greater than 1-log10. Almost 60% of remaining SARS-CoV-2 RNA and more than 70% of remaining HAdV DNA left the system in the sludge, demonstrating that both viruses may have affinity for solids. Coliphages showed a much lower affinity to solids, with only 3.7% leaving the system in the sludge. The system performed well in terms of the removal of organic matter and ammoniacal nitrogen, however tertiary treatment would be necessary to provide further pathogen reduction, if the effluent is to be reused in agriculture. To our knowledge, this is the first study that evaluated the reduction and partitioning of SARS-CoV-2 and HAdV through the complete cycle of a wastewater treatment system consisting of a UASB reactor followed by HRAPs.

Pilot-scale demonstration of a novel process integrating Partial Nitritation with simultaneous Anammox, Denitrification and Sludge Fermentation (PN + ADSF) for nitrogen removal and sludge reduction

Anammox process is a cost-effective solution for nitrogen removal, whereas unsatisfactory effluent with nitrate accumulation is usually achieved in treating domestic sewage, owning to the unwanted prevalence of nitrite-oxidizing bacteria (NOB) and the intrinsic nitrate production by anammox bacteria. Herein, a pilot-scale system integrating Partial Nitritation and simultaneous Anammox, Denitrification and Sludge Fermentation (PN + ADSF) process was developed to treat real municipal wastewater. In this process, PN was accomplished in a sequencing batch reactor (SBR) using the strategy of intermittent hydroxylamine addition, while ADSF coupling anammox and heterotrophic denitrification was conducted in an up-flow anaerobic sludge blanket reactor (UASB) to further remove nitrogen. The pilot-scale system achieved total inorganic nitrogen (TIN) concentrations of 10.0 mg N/L in effluent and sludge reduction efficiency of 42.3% simultaneously. The characterization on microbial communities revealed that Candidatus Kuenenia and Thauera were the dominant functional bacteria for anammox and denitrification, respectively. Supported by the slow-release carbon sources from sludge fermentation, heterotrophic denitrification contributed to about 28% of nitrogen removed from the UASB, while anammox played a more important role in nitrogen removal. The pilot-scale demonstration confirmed that the PN + ADSF process is technically feasible for enhanced nitrogen removal and sludge reduction.

Effect of antibiotic mixtures on the characteristics of soluble microbial products and microbial communities in upflow anaerobic sludge blanket

Two upflow anaerobic sludge blanket reactors (UASBs) were used to investigate the effects of three antibiotic mixtures (erythromycin, sulfamethoxazole, and tetracycline) on reactor performance, soluble microbial products (SMPs) composition and microbial community. One reactor (UASBantibiotics) was fed with antibiotic mixtures, whereas another reactor (UASBcontrol) was used as a control without the addition of antibiotic mixtures. Compared with those in UASBcontrol, UASBantibiotics show lower chemical oxygen demand removal efficiency and biogas content. A higher removal efficiency of antibiotic mixtures was obtained in first few stages in UASBantibiotics. The SMPs composition of effluent from the two reactors did not differ significantly, and the main components were protein-like substances, which produced higher fluorescence intensity in UASBantibiotics. Gas chromatography-mass spectrometry analysis revealed that the main compounds identified as SMPs (<580 Da) were alkanes, aromatics and esters, with only 20% similarity of SMPs between UASBantibiotics and UASBcontrol. Antibiotics had a significant effect on the microbial community structure. Notably, in UASBcontrol, hydrogenotrophic methanogens, key microorganisms in anaerobic digestion, had an obvious advantage at all stages compared with UASBantibiotics, whereas acetoclastic methanogen exhibited the opposite pattern. The above results demonstrated that antibiotic mixtures influenced the effluent quality during anaerobic treatment of synthetic wastewater, resulting in changes in the microbial community structure. This study clarified the effect of antibiotic mixtures on the operation of UASBs. It could contribute to identifying potential strategies for improving effluent quality in anaerobic treatment.

A review on upflow anaerobic sludge blanket reactor: Factors affecting performance, modification of configuration and its derivatives.

The upflow anaerobic sludge blanket (UASB) reactor can be considered as one of the promising anaerobic wastewater treatment technologies suitable for the treatment of high-strength wastewater. In the recent period, researchers have focused on the treatment of low-strength wastewater using this technology. This review focuses on the key factors affecting the reactor performance such as hydraulic retention time (HRT), temperature, organic loading rate (OLR), pH and alkalinity, granulation, wastewater characteristics, mixing, and modification to conventional configuration. Start-up and granulation played a major role in the determination of reactor performance, and various theories have been proposed to understand the mechanism of granulation. Correlation between start-up time and OLR was found to be low, as other operating parameters might have been influencing the start-up time. Flowchart depicting the development of UASB reactor over time is included. In the present work, further development and derivatives of the UASB reactor such as static granular bed reactor (SGBR) and expanded granular sludge bed (EGSB) reactor are analyzed. The optimal conditions for UASB for treating various types of substrates was found to be HRT of 3-24 h, OLR of 1-15 kg COD/m3 /d, and operational temperature in mesophilic range (30-40°C). Analysis of various modifications that pave the way for identification of future areas of research to improve reactor performance is also presented.

Part B: Sludge sewage pre-treatment and codigestion Technical Note 5 – Anaerobic co-digestion of domestic sewage and microalgal biomass with and without solar thermal pre-treatment

Sewage treatment plants have been investigated in order to identify sustainable options for managing the by-products. Due to the widespread use of upflow anaerobic sludge blanket reactors (UASB) for the treatment of sewage in Brazil, one of these solutions would be the use of a high rate algal pond as a post-treatment for this effluent. In addition to being efficient in removing pollutants, the microalgal biomass produced can be introduced in the UASB reactor, being co-digested with raw sewage. This practice would increase methane production at UASB. However, little is known about the co-digestion of microalgae and raw sewage in these reactors. This technical note (TN) aims to report the most important aspects of this practice, as well as to clarify the weaknesses and potentialities for future full-scale implementation. This TN also proposes a sustainable way, based on solar radiation, for the thermal treatment of microalgae. Promising results show a 35% to 40% increase in methane production in UASB with microalgae co-digestion with and without pre-treatment, respectively, compared to a control reactor without co-digestion.