Average Organic Loading Rate Research Articles

Partida de reator anaeróbio compartimentado em série com um reator anaeróbio de manta de lodo, utilizando parâmetros de sedimentabilidade para formação da biomassa

RESUMO Este estudo objetivou avaliar a formação da biomassa de boa qualidade tanto no reator anaeróbio compartimentado (RAC) quanto no reator anaeróbio de manta de lodo (UASB), aplicando parâmetros adequados à sedimentação dos sólidos sedimentáveis (SS) presentes na água residuária de suinocultura (ARS). O RAC e o UASB operaram em série com os tempos de detenção hidráulica (TDHs) de 15 e 9h, respectivamente, correspondendo a cargas orgânicas volumétricas (COVs) médias de 53,8 e 36,2 kg.m³.d¹ em termos de DQOT, respectivamente. As eficiências médias de remoção de DBO520°C, durante o processo de partida e formação da biomassa, foram: 68% para RAC e 55% para UASB, e em termos de DQO: 78% para RAC e 70% para UASB, respectivamente. Os autores concluíram que é possível, mediante os parâmetros de sedimentação adotados, formar uma biomassa peletizada, mesmo operando o sistema com altas cargas orgânicas.

Efficient treatment of baker’s yeast wastewater using aerobic membrane bioreactor

A membrane bioreactor (MBR) system based on a dead-end immersed hollow fiber membrane and filamentous fungus Aspergillus oryzae were used for treatment of baker’s yeast wastewater. The fungus was adapted to the wastewater in the bioreactor for two weeks before starting the continuous process. Average organic loading rate of 4.2 kg COD/m3.d was entered the bioreactor. MBR system was able to reduce the COD and BOD5 of the wastewater from 5000 and 1400 mg/L to 488 and 70 mg/L, respectively, over a period of 45 days, while the turbidity of the wastewater reduced from 134-282 NTU to less than 2.5 NTU in the permeate stream. Critical flux and a suitable operating flux were determined as 6.7 and 5 L/m2 h, respectively. The obtained results confirm that the MBR system was able to efficiently reduce the turbidity and suspended solid of the wastewater by 99.4% and 98.3%, respectively, resulting in a clear effluent.

음식물류 폐기물 처리를 위한 준 회분식 액순환 건식 혐기성 소화법에 대한 기초연구

In this study, the experiment was carried out to produce methane by applying Semi-Continuous Leachate Recirculation Anaerobic Digestion System fed with source separated food waste from school cafeteria. There were two systems and each system consisted of a bioreactor and a liquid tank. Each bioreactor had a screen near the bottom of the reactor. 2.5L of separated liquid was transferred to the liquid tank for 30min each day by using a tubing pump and the liquid from the liquid tank was pumped to the bioreactor at the upper of the bioreactor as soon as the transfer was ended. Through this circulation, the liquid having high concentration of VFAs was supplied to the top of bioreactor. At the beginning of the experiment, food waste/inoculum anaerobic sludge volume ratio was 2:8 that is 9g VS/L of OLR(Organic Loading Rate). Feeding was conducted every two weeks. Experimental results showed that the contents of moisture, combustible matter, ash were 65.91%, 32.73%, and 1.36%, respectively. Two different food waste loading were studied. The average organic loading rates were 3.51g VS/d for System A and 3.86g VS/d for System B, respectively. The average produced methane based on food waste fed to bioreactor were observed as 6.30m 3 CH4/kgVS⋅d for system A and 4.94m 3 CH4/kgVS⋅d for System B, respectively.

Anaerobic up flow fluidized bed reactor performance as a primary treatment unit in domestic wastewater treatment

The fluidized bed UASB performance was studied in this experiment as a primary unit the anaerobic unit the advantage of better generated sludge characteristics and smaller tank volume.The reactor performance was investigated for the treatment of domestic wastewater with unexpected industrial water flows at different operational temperatures (14–25°C) and loading rates. For each temperature range the reactor performance was studied under different hydraulic loadings HRT (6, 4, 2.5h).The best methane yield rate and COD total removal rate are 0.285l/g COD total and 70.82% respectively at warm working temperature 19°C with OLR 7.76kg COD/m3/day and HRT 6h.On the low temperature operation, the average COD removal of the reactor was 55.28% and 50.33% for HRT of 4h and 2.5h respectively. The methane production dropped to 0.1623 & 0.0988L CH4/g COD with average organic loading rate of 5.34 & 10kg COD/m3/day for HRT of 4h and 2.5h respectively.The efficiencies of Total nitrogen removal ranged between 2.23 and 10.83% with an apparent decrease during the low temperature high rate stages. Nitrite removal was in the range of (23.08–77)% with up to the 2mg/L in the effluent water when obtaining high organic loading and warm temperature. These results demonstrated that the domestic wastewater could be anaerobically treated in a fluidized bed UASB reactor with very low HRT reaching 2.5h.

Two-Phase Anaerobic Digestion Model of a Tannery Solid Waste: Experimental investigation and Modeling with ANFIS

Anaerobic digestion of limed fleshing solid waste from leather-processing industry and effluent treatment liquid waste was studied in a two-phase digester. The hydrolysis and acidification stages resulted in the formation of volatile fatty acid (VFA), where the maximum concentration of total VFA observed in the acidogenic reactor was 18,225mg/L and the average VFA concentration was 10,574mg/L for hydraulic retention time (HRT) of 10days. The hydrolyzed predigested material was tested in a methanogenesis reactor for biogas generation at HRT of 20 days. The two-phase process of the digestion system has been modeled using adaptive neuro-fuzzy inference system (ANFIS) with HRT, pH and organic loading rate (OLR) as input parameters and cumulative gas production as output parameter. The average CH4 production rate over the entire study period was 0.31m3CH4/kg VS destroyed and 0.15m3 CH4/kg VS fed at an overall average OLR of 1.05 ± 0.05kg VS/m3day. Modeling with ANFIS using HRT, OLR and pH as inputs and cumulative production of gas as output produced a mean-square error of only 0.00049 which is relatively more accurate with reference to available literature.

Effects of loading rate and aeration on nitrogen removal and N2O emissions in intermittently aerated sequencing batch reactors treating slaughterhouse wastewater at 11°C.

This study aimed to find optimal operation conditions for nitrogen removal from high strength slaughterhouse wastewater at 11°C using the intermittently aerated sequencing batch reactors (IASBRs) so as to provide an engineering control strategy for the IASBR technology. Two operational parameters were examined: (1) loading rates and (2) aeration rates. Both the two parameters affected variation of DO concentrations in the IASBR operation cycles. It was found that to achieve efficient nitrogen removal via partial nitrification-denitrification (PND), "DO elbow" point must appear at the end of the last aeration period. There was a correlation between the ammonium oxidizing bacteria (AOB)/nitrite oxidizing bacteria (NOB) ratio and the average DO concentrations in the last aeration periods; when the average DO concentrations in the last aeration periods were lower than 4.86mg/L, AOB became the dominant nitrifier population, which benefited nitrogen removal via PND. Both the nitrogen loading rate and the aeration rate influenced the population sizes of AOB and NOB. To accomplish efficient nitrogen removal via PND, the optimum aeration rate (A, Lair/min) applied can be predicted according to the average organic loading rates based on mathematical equations developed in this study. The research shows that the amount of N2O generation in the aeration period was reduced with increasing the aeration rate; however, the highest N2O generation in the non-aeration period was observed at the optimum aeration rates.

Influence of hydrothermal pretreatment on microalgal biomass anaerobic digestion and bioenergy production

Microalgal biomass grown in wastewater treatment raceway ponds may be valorised producing bioenergy through anaerobic digestion. However, pretreatment techniques seem to be necessary for enhancing microalgae methane yield. In this study, hydrothermal pretreatment was studied prior to batch and continuous reactors. The pretreatment increased organic matter solubilisation (8–13%), anaerobic digestion rate (30–90%) and final methane yield (17–39%) in batch tests. The highest increase was attained with the pretreatment at 130 °C for 15 min, which was attested in a laboratory-scale continuous reactor operated at a hydraulic retention time of 20 days with an average organic loading rate of 0.7 g VS/L·day. The methane yield increased from 0.12 to 0.17 L CH4/g VS (41%) in the pretreated digester as compared to the control. Microscopic images of microalgal biomass showed that pretreated cells had unstructured organelles and disrupted cell wall external layer, which may enhance the hydrolysis. Indeed, images of the pretreated reactor digestate showed how cells were more degraded than in the control reactor.

Influence of inoculum on growth and retention of the biomass in anaerobic filters

In this study we evaluated, on bench scale, two anaerobic filters of equal configuration and using coconut shell as support material, for the treatment of the wastewater generated in cassava’s starch extraction process. Considering that in the study area the inoculum available in enough quantity is cow manure, this inoculum was used alone (Reactor 1) and mixed with granular sludge in a ratio of 1:1 (Reactor 2). The influence of inoculum was evaluated in the performance of the anaerobic filters as well as in the biomass adaptation to the substrate and the prevalent growth on support material. Both reactors showed potential for the treatment of this type of wastewater, with a Hydraulic Retention Time (HRT) of 12 hours, an average Organic Loading Rate (OLR) of 7.0 kg COD/m3*d and a Buffer Index (BI) that varied from 0.20 to 0.35. The increase up to 50% in the Specific Methanogenic Activity (SMA) at the end of the start-up in both reactors, confirmed the adequate biomass adaptation to the substrate as a result of the control of buffer capacity, and the higher values in the R2, showed that cow manure mixed with granular sludge improved methane production and process efficiency. It was found that the occluded biomass had greater activity than the attached one; this showed that the support material allowed the development of a greater proportion of active biomass within the interstices.

Semi-continuous anaerobic co-digestion of cow manure and steam-exploded Salix with recirculation of liquid digestate

The effects of recirculating the liquid fraction of the digestate during mesophilic anaerobic co-digestion of steam-exploded Salix and cow manure were investigated in laboratory-scale continuously stirred tank reactors. An average organic loading rate of 2.6 g VS L−1 d−1 and a hydraulic retention time (HRT) of 30 days were employed. Co-digestion of Salix and manure gave better methane yields than digestion of manure alone. Also, a 16% increase in the methane yield was achieved when digestate was recirculated and used instead of water to dilute the feedstock (1:1 dilution ratio). The reactor in which the larger fraction of digestate was recirculated (1:3 dilution ratio) gave the highest methane yields. Ammonia and volatile fatty acids did not reach inhibitory levels, and some potentially inhibitory compounds released during steam explosion (i.e., furfural and 5-hydroxy methyl furfural) were only detected at trace levels throughout the entire study period. However, accumulation of solids, which was more pronounced in the recycling reactors, led to decreased methane yields in those systems after three HRTs. Refraining from the use of fresh water to dilute biomass with a high-solids content and obtaining a final digestate with increased dry matter content might offer important economic benefits in full-scale processes. To ensure long-term stability in such an approach, it would be necessary to optimize separation of the fraction of digestate to be recirculated and also perform proper monitoring to avoid accumulation of solids.

Mathematical modeling of bio-hydrogen production from starch wastewater via up-flow anaerobic staged reactor

Hydrogen production from starch wastewater industry via up-flow anaerobic staged reactor was investigated. The reactor was operated at an average organic loading rate of 13.17 ± 8.35g COD/L d and hydraulic retention time of 8 h. The reactor achieved chemical oxygen demand (COD) and carbohydrate removal efficiencies of 84 and 92%, respectively. The total volatile fatty acids increased from 58.5±30.0 (influent) to 235.6±190.8 mg/L in the treated effluent, indicating that acidogenesis bacteria were dominant in the reactor. The system achieved maximum hydrogen production rate (HPR) and hydrogen yield of 2.48 L H2/d and 8.8 mL H2/g CODremoved, respectively. Simulated model tracks the experimental data with a correlation coefficient (R2 = 0.893). Maximum substrate utilization rate (μmax,s) and maximum volumetric HPR (μmax,h) were calculated at different food to micro-organisms (F/M) ratios of 0.15, 0.31, 0.46, 0.62, and 0.93g COD/g VSS. Results showed that μmax,s increased to −0.76g COD/L h at F/M ratio of 0.46, and then remained relatively constant at a value of −0.68g COD/L h. Similar trends were observed for HPR, where it peaked (μmax,h of 93.89 mL H2/h) at F/M ratio of 0.46.

Packed bed up-flow anaerobic sludge blanket combined with multistage sand fine roughing filtration for municipal wastewater treatment and reuse

There is a high potential for reuse of treated wastewater due to the shortage of renewable water resources for agricultural purposes in many countries of the world. To achieve this goal, an integrated anaerobic pilot plant treatment system treating almost 10 m 3 /day of wastewater was designed, manufactured and installed in a nearby wastewater treatment plant. The treatment scheme consists of a packed bed up-fl ow anaerobic sludge blanket (P-UASB) with corrugated lamella sheets, followed by inclined plate settler (IPS). However, to obtain a treated effl uent amenable for reuse, post-treatment was carried out using a multi-stage roughing fi ne fi ltration unit (MSRFF). The pilot plant was operated at average hydraulic fl ow rate of 10 m 3 /day with average organic loading rate of 3.27 kg chemical oxygen demand (COD) m 3 /day. Two retention times in P-UASB namely, 4 and 6 h were investigated. The performance of the treatment scheme was monitored via physico-chemical as well as bacteriological and parasitological analysis. Treatment of wastewater by P-UASB followed by IPS produced a high quality effl uent. Average removal rates of COD, biochemical oxygen demand (BOD) and total suspended solids (TSS) were 75, 70.6 and 91.3, respectively, with average corresponding residual values of 75, 58 and 18 mg/l. However, to obtain sustainable quality of treated effl uent for reuse, post-treatment using MSRFF improved the quality of treated wastewater both chemically and biologically. The average residual concentrations of COD, BOD and TSS were 60, 34 and 10.9 mg/l, respectively, while almost complete removal of Fecal Coliforms was achieved. The treatment scheme proved to be a very promising approach for wastewater treatment for reuse in agricultural purposes.

Innovative sustainable anaerobic treatment for wastewater

The main objective of this study is to demonstrate and implement a cost-effective system for low-strength municipal wastewater treatment in rural areas. An integrated compact anaerobic treatment pilot plant unit was designed, constructed and operated for almost two years. The pilot plant consists of three successive compartments mainly: primary sedimentation (PS), packed bed upflow anaerobic sludge blanket (P-UASB) and inclined plate settler. The pilot plant was operated continuously at a hydraulic loading rate of 6 m3/day, average organic loading rate of 2.03 kg COD/m3/day and average retention time of 4 h at the P-UASB and a total retention time 6 h for the integrated treatment unit. The performance of the treatment train was monitored via physicochemical as well as bacteriological and parasitological analysis. The average removal rates of chemical oxygen demand, biological oxygen demand and total suspended solids were 78, 79 and 91%, respectively, with corresponding average residual values of 71 mgO2/L, 39 mgO2/L and 18 mg/L. Bacterial analysis indicated that great majorities were removed but still some residuals exist. The treated wastewater, after disinfection, was complying with the Egyptian Code for wastewater reuse in restricted irrigation. The results indicated that the total life cost of the pilot plant, during the research period, proved to be a cost-effective process for treating low-strength wastewater.

Identical full-scale biogas-lift reactors (BLRs) with anaerobic granular sludge and residual activated sludge for brewery wastewater treatment and kinetic modeling

Two identical full-scale biogas-lift reactors treating brewery wastewater were inoculated with different types of sludge to compare their operational conditions, sludge characteristics, and kinetic models at a mesophilic temperature. One reactor (R1) started up with anaerobic granular sludge in 12 weeks and obtained a continuously average organic loading rate (OLR) of 7.4 kg chemical oxygen demand (COD)/(m3·day), COD removal efficiency of 80%, and effluent COD of 450 mg/L. The other reactor (R2) started up with residual activated sludge in 30 weeks and granulation accomplished when the reactor reached an average OLR of 8.3 kg COD/(m3·day), COD removal efficiency of 90%, and effluent COD of 240 mg/L. Differences in sludge characteristics, biogas compositions, and biogas-lift processes may be accounted for the superior efficiency of the treatment performance of R2 over R1. Grau second-order and modified StoverKincannon models based on influent and effluent concentrations as well as hydraulic retention time were successfully used to develop kinetic parameters of the experimental data with high correlation coefficients (R2 > 0.95), which further showed that R2 had higher treatment performance than R1. These results demonstrated that residual activated sludge could be used effectively instead of anaerobic granular sludge despite the need for a longer time.

Nitrogen removal from slaughterhouse wastewater through partial nitrification followed by denitrification in intermittently aerated sequencing batch reactors at 11°C

This study is aimed to examine the removal of nitrogen from high strength slaughterhouse wastewater at 11°C via partial nitrification followed by denitrification (PND), using the intermittently aerated sequencing batch reactor (IASBR) technology. The slaughterhouse wastewater contained chemical oxygen demand (COD) of 6068 mg/L, total nitrogen (TN) of 571 mg/L, total phosphorus (TP) of 51 mg/L and suspended solids of 1.8 g/L, on average. The laboratory-scale IASBR reactors had a working volume of 8 L and was operated at an average organic loading rate of 0.61 g COD/(L·d). At the cycle duration of 12 h, COD was efficiently removed under three aeration rates of 0.4, 0.6 and 0.8 L air/min. Among the three aeration rates, the optimum aeration rate was 0.6 L air/min with removals of COD, TN, and TP of 98%, 98%, and 96%, respectively. The treated wastewater met the Irish emission standards. The microbial community analysis by fluorescence in situ hybridization shows 12±0.4% of ammonium oxidizing bacteria, and 7.2±0.4% of nitrite oxidizing bacteria in the general bacteria (EUB) in the activated sludge at the aeration rate of 0.6 L air/min, leading to efficient partial nitrification. PND effectively removed nitrogen from slaughterhouse wastewater at 11°C, but PND efficiency was dependent on the aeration rate applied. PND efficiencies were up to 75.8%, 70.1% and only 25.4% at the aeration rates of 0.4, 0.6, and 0.8 L air/min.

Anaerobic digestion of peel waste and wastewater for on site energy generation in a citrus processing facility

A citrus processing facility produces significant quantities of both peel waste and wastewater. A leach – bed batch anaerobic digester was operated successfully at thermophilic (55 °C) temperature for biogasification of citrus peel waste. The retention time in the digester was 25 days. The citrus processing wastewater was digested in a thermophilic DSFF (down flow stationary fixed film) anaerobic reactor fed continuously and operated for 76 days. At an average organic loading rate of 0.51 kg sCOD m−3 d−1 the hydraulic retention time was 16 days. No long term toxicity issues due to limonene were observed during digestion of both citrus waste feedstocks. Biogasification yielded, 0.116 m3 methane at STP kg−1 peel waste received and 2.1 m3 at STP m−3 wastewater received. An energy analysis showed that in a citrus processing plant handling 600 tons per day of fruits, the biogas produced from the waste streams is more than sufficient to meet all the electricity and fuel demands. Excess electricity generated from biogas may be sold generating estimated revenues of more than a $1 million annually (at electricity sale price of $0.04/kWhe).

Eficiência de sistemas alagados construídos na remoção de poluentes de águas residuárias de indústria de laticínios

Objetivou-se avaliar a eficiência de sistemas alagados construídos (SACs), cultivados com dois diferentes capins e cinco taxas de carregamento orgânico (TCOs) na remoção de poluentes de águas residuárias de indústria de laticínios (ARL). Para isso, unidades experimentais foram constituídas por um SAC sem vegetação (SV), cinco SACs cultivados com capim-elefante (SACs-CF) e cinco SACs cultivados com capim-tifton 85 (SACs-CT), com escoamento subsuperficial horizontal. A ARL foi aplicada numa vazão média de 60 L d-1 e tempo de residência hidráulica de 4,8 dias e TCOs de 66; 130; 190; 320 e 570 kg ha-1 d-1 de DBO5. Os SACs mostraram-se eficientes na remoção da DBO, DQO e dos SSTs, STs e NTKs, porém foram pouco eficientes na remoção de P-total, K e Na da ARL. As duas forrageiras avaliadas apresentaram semelhante influência no processo de remoção de DBO5, DQO, ST, SST, P-total, K e Na, quando comparadas com sistemas que operaram com mesma taxa de carregamento orgânico, tendo as remoções de DBO e DQO ficado na faixa de 79 a 96 % e 85 a 97 %, respectivamente. O SAC sem vegetação (SV) apresentou desempenho semelhante ao dos SACs vegetados na remoção de DBO5, DQO, ST, SST e Na, enquanto o cultivado com capim-tifton foi mais eficiente na remoção de NTK.

The Concept of Wastes to Energy Using Sugary Wastes

Abstract: This study was designed using actual effluent from the sugary mills in an Up-flow Anaerobic Sludge Blanket (UASB) Reactor to evaluate treatability performance. The reactor was started-up in step-wise loading rates beginning from 0.05kg carbon oxygen demand (COD)/m3-day to 3.50kg-COD/m3-day. The hydraulic retention time (HRT) was slowly decreased from 96 hrs to eight hrs. It was observed that the removal efficiency of COD of more than 73% can be easily achieved at an HRT of more than 16 hours corresponding to an average organic loading rate (OLR) of 3.0kg-COD/m3-day, at neutral pH and constant temperature of 29°C. The average VFAs (volatile fatty acids) and biogas production was observed as 560mg/L and 1.6L/g-CODrem-d, respectively. The average methane composition was estimated as 62%. The results of this study suggest that the treatment of sugar mills effluent with the anaerobic technology seems to be more reliable, effective and economical.DOI: http://dx.doi.org/10.3126/hn.v9i0.7075 Hydro Nepal Vol.9 July 2011 57-62

Open trickling filter: an innovative, cheap and simple form of post-treatment of sanitary effluents from anaerobic reactors in small communities

We aimed to evaluate the performance and cost savings of an innovative design of a trickling filter (TF) for small population sizes, developed at the Federal University of Minas Gerais, Brazil referred to as an open trickling filter (OTF). The OTF had no side walls and no perforated bottom slab, and was applied for the post-treatment of sanitary sewage from an upflow anaerobic sludge blanket (UASB) reactor. The OTF had crushed-stone packing (3.5 m high) and was operated with an average surface hydraulic loading rate of 4.1 m3 m−2 d−1 and an average volumetric organic loading rate of 0.10 kg BOD m−3 d−1 (biochemical oxygen demand). The average concentrations obtained at the OTF effluent were 48 mg TSS L−1 (total suspended solids), 132 mg COD L−1 (chemical oxygen demand), 51 mg BOD L−1, 19 mg TKN L−1 (total Kjeldahl nitrogen), 16 mg NH4+-N L−1 and 10 mg NO3−-N L−1, complying with local discharge standards. Analysis of the construction costs indicated savings of 74% compared to conventional TF. Based on the performance, compactness, simplicity and reduced capital costs, it is believed that the proposed OTF is a good alternative for small communities, especially in developing countries.

Effect of surfactant on styrene removal from waste gas streams in biotrickling filters

AbstractBACKGROUND: The performance of two biotrickling filters (BTFs) was evaluated for styrene removal from gas streams at the start‐up period and at a pseudo‐steady‐state under various operating conditions.RESULTS: The BTFs exceeded 99% removal efficiency within 19 days when the average inlet styrene concentration was 250 mg m−3 and gas empty bed retention time (EBCT) was 30.0 s. The effect of a surfactant, Triton X‐100, on styrene removal was examined by comparative experiments in which one biofilter was fed with nutrient solution with the surfactant while the other without the surfactant, and the average organic loading rate of styrene was set at 65.3, 100.9 and 201.7 g styrene m−3 h−1, respectively. Results showed that the corresponding average removal efficiency was 87%, 70% and 50% for the BTF without surfactant, while the average removal efficiency for the BTF with surfactant was 96%, 92% and 82%. Excessive biomass accumulation was observed in the medium when the styrene loading rate was high. However, the biomass density within the BTF medium when the surfactant was added remained stable during the whole period of the operation.CONCLUSION: These results demonstrated that the use of Triton X‐100 can improve the degradation of styrene and control the excessive biomass accumulation. Copyright © 2012 Society of Chemical Industry

Molecular characterization of bacterial communities in algal–bacterial photobioreactors treating piggery wastewaters

The influence of the loading rate and the seasonal environmental conditions on the bacterial communities established in High Rate Algal Ponds (HRAPs) treating diluted swine manure was investigated using 16S rRNA Denaturing Gradient Gel Electrophoresis (DGGE) and further phylogenetic analysis. Two HRAPs were successfully operated at different loading rates (10 and 20 times diluted swine manure, resulting in average Surface Organic Loading Rates (SOLR) ranging from 13 to 99gm−2d−1 and from 21 to 180gm−2d−1, respectively) for 9 months. The DGGE analysis revealed a high diversity of bacteria symbiotically living with microalgae. The environmental conditions rather than the organic loading rate were the most significant factors determining the bacterial community structure. Hence, despite a higher biodiversity was recorded in summer, both HRAPs presented a similar community regardless of their different organic loading. Most of the species (≈54%) belonged to Verrucomicrobium, an ubiquitous phylum of aerobic bacteria commonly found in eutrophic environments. Firmicutes and Proteobacteria (Gammaproteobacteria) were the other dominant phyla. Some of the bacteria present in the HRAPs were highly resistant to UV radiation and floc-forming species, which might explain the reasonable good settling characteristics of the algal–bacterial biomass in the ponds. The present work provides new insights on the complex interactions between microalgae and bacteria in algal-based wastewater treatment systems.