Microbial community dynamics and electricity generation in MFCs inoculated with POME sludges and pure electrogenic culture

Palm Oil Mill Effluent (POME) requires treatment before disposal due to its high organic matter content. In this study, the electrical performance and wastewater treatment efficiency were evaluated for Microbial Fuel Cells (MFC) treating unsterile POME with chemical oxygen demand (COD) from 200 to 10 000 mg/L. Since the inoculum type is a key factor in MFC performance, three types of sludge (methanogenic sludge (MS), facultative sludge (FS), and dry sludge (DS), obtained from the current POME treatment ponds were evaluated as inoculum. Dry sludge (DS) developed a maximum power output of 3.30 W/m³ by oxidizing 71% out of the COD provided by POME (1000 mg/L). Also, raw POME microbiota contributed to an enrichment of the community in DS inoculum along with the operation, in which Geobacter was the predominant genus reaching a current generation of 247 mA/m² and a power density of 2.36 W/m³. Conversely, pure electrogenic (Shewanella sp.) inoculation led to a diversification process, resulting in a lower current generation of 52 mA/m² and a power density of 0.10 W/m³. Consequently, microbial community dynamics revealed that MFC inoculation tends to a microbial equilibrium wherein generation of high current density was achieved by gradual microbial enrichment rather than external electrogenic invasion.     

Effect of organic fraction of municipal solid waste addition to high rate activated sludge system for hydrogen production from carbon rich waste sludge

Municipal solid waste has been used for bio-methane production for many years. However, both methane and carbon dioxide that is produced during bio-methanization increases the greenhouse gas emissions; therefore, hydrogen production can be one of the alternatives for energy production from waste. Hydrogen production from the organic substance was studied in this study with the waste activated sludge from the municipal wastewater treatment. High rated activated sludge (HRAS) process was applied for the treatment to reduce energy consumption and enhance the organic composition of WAS. The highest COD removal (76%) occurred with the 12 g/L organic fraction of municipal solid waste (OFMSW) addition at a retention time of 120 min. The maximum hydrogen and methane yields for the WAS was 18.9 mL/g VS and 410 mL/g VS respectively. Total carbon emission per g VS of the substrate (OFMSW + waste activated sludge) was found as 0.087 mmol CO₂ and 28.16 mmol CO₂ for dark fermentation and bio-methanization respectively. These kinds of treatment technologies required for the wastewater treatment plantcompensate it some of the energy needs in a renewable source. In this way, the HRAS process decreases the energy requirement of wastewater treatment plant, and carbon-rich waste sludge enables green energy production via lower carbon emissions.     

Metagenomic-based analysis of biofilm communities for electrohydrogenesis: From wastewater to hydrogen

Microbial electrolysis cells (MECs) use exoelectrogenic microorganisms to convert organic matter into H₂, although yields can vary significantly with environmental conditions, likely due to variations in microbial communities. This study was undertaken to better understand how microbial communities affect reactor function. Using wastewater as inoculum, 15 MEC reactors were operated for >50 days and subsequently five reactors were selected for further analysis. Solution (26 mL) was collected every 3–4 days for DNA extraction. DNA was hybridized to GeoChip, a comprehensive functional gene array, to examine differences in the reactor microbial communities. A large variety of microbial functional genes were observed in all reactors. Performances ranged from poor (0.1 ± 0.1 mL) to high (12.2 ± 1.0 mL) H₂ production, with a maximum yield of 5.01 ± 0.43 mol H₂/mol_glucose. The best performance was associated with higher cytochrome c genes, considerably higher exoelectrogenic bacteria (such as Shewanella, Geobacter), less methanogens and less hydrogen-utilizing bacteria. The results confirmed the possibility to obtain an effective community for hydrogen production using wastewater as inoculum. Not like fermentation, hydrogen production was significantly controlled by electron transporting process in MECs. GeoChip findings suggested that biofilm formation can be highly stochastic and that presence of dissimilatory metal-reducing bacteria and antagonistic methanogens is critical for efficient hydrogen production in MEC reactors.     

Anodic inoculum pre-treatment by extracts of Azadirachta indica leaves and Allium sativum peels for improved bioelectricity recovery from microbial fuel cell

The electrogenic bacterial consortia enrichment in the anodic chamber play a crucial role in determining the efficiency of microbial fuel cell (MFC). In order to use mix anaerobic culture enriched with active electrogenic species as inoculum, suppression of methanogens is important. This investigation focuses on potential of extracts of Azadirachta indica (Neem) leaves and Allium sativum (Garlic) peels in inhibiting activity of methanogenic microorganisms in the mixed anaerobic sludge. Specific methane yields of sludge treated with neem leaves extract, garlic peel extract and untreated sludge were found to be 0.068 ± 0.08 L CH₄/g VSS.d, 0.073 ± 0.08 L CH₄/g VSS.d, and 0.193 ± 0.08 L CH₄/g VSS.d, respectively. However, the MFC operated with these pre-treated inoculums gave respective power densities of 5.6 W/m³, 5.0 W/m³, and 2.65 W/m³, respectively. Hence, it can be inferred that pre-treatment of mixed anaerobic sludge using neem leaves and garlic peels extract can be effective in enhancing power produced from MFCs.     

Enhanced microbial oil production by activated sludge microorganisms from sugarcane bagasse hydrolyzate

The use of sugarcane bagasse hydrolyzate as a carbon source for enhanced oil production by activated sludge microbial cultures was investigated. Cultivation of raw activated sludge inoculum using pure xylose as carbon source was necessary prior to bagasse hydrolyzate feeding for microbial acclimation to this pentose sugar, the major component of the hydrolyzate. Lipid contents from 40 to 47% (dry cell weight) were achieved under high C:N ratio following bagasse hydrolyzate feeding; however nutrient supplementation was found to be necessary in order to maintain viable cell biomass levels (>10 g/L) to achieve a high lipid titer (7.62 g/L). Hence, a process involving sequential batch feeding of hydrolyzate with and without nutrients was proposed and simulated using the Logistic and Luedeking–Piret models. Analysis of the product lipids showed up to 50% saponifiable fractions and dominance of C₁₆ and C₁₈ fatty acids, demonstrating their suitability as biofuel feedstock.     

The effects of seed sludge and hydraulic retention time on the production of hydrogen from a cassava processing wastewater and glucose mixture in an anaerobic fluidized bed reactor

The potential for co-fermentation of a cassava processing wastewater and glucose mixture was studied in anaerobic fluidized bed reactors. The effects of different hydraulic retention times (HRTs) (10–2 h) and varying sources of inoculum are reported. The sludge from a UASB reactor that had been used to treat poultry slaughterhouse wastewater (SP) resulted in the highest yields of hydrogen (HY) and ethanol (EtOHY) of 1.0 mmol H₂ g⁻¹ COD (10 h) and 3.0 mmol EtOH g⁻¹ COD (6 h). The sludge from a UASB reactor used for the treatment of swine wastewater (SW) resulted in a maximum HY of 0.65 mmol H₂ g⁻¹ COD (6 h) and EtOHY of 2.1 mmol g⁻¹ COD (10 and 8 h). Methane was produced with a maximum production of 9.68 L CH₄ d⁻¹ L⁻¹. Based on phylogenetic analysis of 16S rRNA, bacteria and methanogenic archaea similar to Lactobacillus and Methanobacterium, respectively, were identified.     

Co-hydrothermal gasification of microbial sludge and algae Kappaphycus alvarezii for bio-hydrogen production: Study on aqueous phase reforming

In this study, wastewater obtained from a sewage treatment plant was treated successively by using microbial consortium and macroalgae Kappaphycus alvarezii to generate microbial sludge and algal biomass. The production of green fuel was carried out via co-gasification of microbial sludge and macroalgae Kappaphycus alvarezii for a duration of 60 min, feedstock to solvent ratio (5 to 20 g of feedstock in 200 mL), sludge to algae ratio (ranging from 1:1 to 3:1) and temperature (300–400 °C) respectively. Maximum bio-hydrogen yield was 36.1% and methane yield was 38.4% at a temperature of 360 °C at a feedstock to solvent ratio of 15:200 g/mL and sludge to algae ratio of 2:1 individually. The liquid by product of co-gasification process was later subjected to photocatalytic reforming, resulted in an enhanced hydrogen composition of 61.25%.     

Effects of pretreatment methods on cassava wastewater for biohydrogen production optimization

Batch production of biohydrogen from cassava wastewater pretreated with (i) sonication, (ii) OPTIMASH BG^® (enzyme), and (iii) α-amylase (enzyme) were investigated using anaerobic seed sludge subjected to heat pretreatment at 105 °C for 90 min. Hydrogen yield at pH 7.0 for cassava wastewater pretreated with sonication for 45 min using anaerobic seed sludge was 0.913 mol H₂/g COD. Results from pretreatment with OPTIMASH BG^® at 0.20% and pH 7 showed a hydrogen yield of 4.24 mol H₂/g COD. Superior results were obtained when the wastewater was pretreated with α-amylase at 0.20% at pH 7 with a hydrogen yield of 5.02 mol H₂/g COD. In all cases, no methane production was observed when using heat-treated sludge as seed inoculum. Percentage COD removal was found to be highest (60%) using α-amylase as pretreatment followed by OPTIMASH BG^® at 54% and sonication (40% reduction rate). Results further suggested that cassava wastewater is one of the potential sources of renewable biomass to produce hydrogen.     

Impact of the microbial inoculum source on pre-treatment efficiency for fermentative H2 production from glycerol

Hydrogen (H₂) production by dark fermentation can be performed from a wide variety of microbial inoculum sources, which are generally pre-treated to eliminate the activity of H₂-consuming species and/or enrich the microbial community with H₂-producing bacteria. This paper aims to study the impact of the microbial inoculum source on pre-treatment behavior, with a special focus on microbial community changes. Two inocula (aerobic and anaerobic sludge) and two pre-treatments (aeration and heat shock) were investigated using glycerol as substrate during a continuous operation. Our results show that the inoculum source significantly affected the pre-treatment efficiency. In aerobic sludge no pre-treatment is necessary, while in anaerobic sludge the heat pre-treatment increased H₂ production but aeration caused unstable H₂ production. In addition, biokinetic control was key in Clostridium selection as dominant species in all microbial communities. Lower and unstable H₂ production were associated with a higher relative abundance of Enterobacteriaceae family members. Our results allow a better understanding of H₂ production in continuous systems and how the microbial community is affected. This provides key information for efficient selection of operating conditions for future applications.     

Simultaneous thermophilic hydrogen production and phenol removal from palm oil mill effluent by Thermoanaerobacterium-rich sludge

Thermoanaerobacterium-rich sludge was used for hydrogen production and phenol removal from palm oil mill effluent (POME) in the presence of phenol concentration of 100–1000 mg/L. Thermoanaerobacterium-rich sludge yielded the most hydrogen of 4.2 L H₂/L-POME with 65% phenol removal efficiency at 400 mg/L phenol. Butyric acid and acetic acid were the main metabolites. The effects of oil palm ash, NH₄NO₃ and iron concentration (Fe²⁺) on hydrogen production and phenol removal efficiency from POME by Thermoanaerobacterium-rich sludge was investigated using response surface methodology (RSM). The RSM results indicated that the presence of 0.2 g Fe²⁺/L, 0.3 g/L NH₄NO₃ and 20 g/L oil palm ash in POME could improved phenol removal efficiency, with predicted hydrogen production and phenol removal efficiency of 3.45 L H₂/L-POME and 93%, respectively. In a confirmation experiment under optimized conditions highly reproducible results were obtained, with hydrogen production and phenol removal efficiency of 3.43 ± 0.12 L H₂/L-POME and 92 ± 1.5%, respectively. Simultaneous hydrogen production and phenol removal efficiency in continuous stirred tank reactor at hydraulic retention time (HRT) of 1 and 2 days were 4.0 L H₂/L-POME with 85% and 4.2 L H₂/L-POME with 92%, respectively. Phenol degrading Thermoanaerobacterium-rich sludge comprised of Thermoanaerobacterium thermosaccharolyticum, Thermoanaerobacterium aciditolerans, Desulfotomaculum sp., Bacillus coagulans and Clostridium uzonii. Phenol degrading Thermoanaerobacterium-rich sludge has great potential to harvest hydrogen from phenol-containing wastewater.     

Microbial hydrogen production from sewage sludge bioaugmented with a constructed microbial consortium

A constructed microbial consortium was formulated from three facultative H₂-producing anaerobic bacteria, Enterobacter cloacae IIT-BT 08, Citrobacter freundii IIT-BT L139 and Bacillus coagulans IIT-BT S1. This consortium was tested as the seed culture for H₂ production. In the initial studies with defined medium (MYG), E. cloacae produced more H₂ than the other two strains and it also was found to be the dominant member when consortium was used. On the other hand, B. coagulans as a pure culture gave better H₂ yield (37.16 ml H₂/g COD_consumed) than the other two strains using sewage sludge as substrate. The pretreatment of sludge included sterilization (15% v/v), dilution and supplementation with 0.5% w/v glucose, which was found to be essential to screen out the H₂ consuming bacteria and ameliorate the H₂ production. Considering (1:1:1) defined consortium as inoculum, COD reduction was higher and yield of H₂ was recorded to be 41.23 ml H₂/g COD_reduced. Microbial profiling of the spent sludge showed that B. coagulans was the dominant member in the constructed consortium contributing towards H₂ production. Increase in H₂ yield indicated that in consortium, the substrate utilization was significantly higher. The H₂ yield from pretreated sludge (35.54 ml H₂/g sludge) was comparatively higher than that reported in literature (8.1–16.9 ml H₂/g sludge). Employing formulated microbial consortium for biohydrogen production is a successful attempt to augment the H₂ yield from sewage sludge.     

Fermentative H2 production using a switchgrass steam exploded liquor fed to mixed anaerobic cultures: Effect of hydraulic retention time,linoleic acid and nitrogen sparging

Fermentative hydrogen (H₂) production from a steam exploded switchgrass liquor using inhibited mixed anaerobic microbial communities was studied in upflow anaerobic sludge blanket reactors (UASBRs). Increasing the H₂ yield was accomplished by treating the inoculum with linoleic acid (LA), varying the hydraulic retention time (HRT) and sparging liquid phase with nitrogen (N₂). A maximum H₂ yield of 2.56 ± 0.10 mol mol⁻¹ hexose, was obtained at a 6 h HRT in LA treated cultures sparged with N₂. Sparging or LA treatment alone was able to enhance the H₂ yield by 46 ± 5% and 38 ± 3%, respectively, in comparison to control cultures operating at a 6 h HRT. Of the different methods employed, N₂ sparging in combination with LA treatment proved to be more effective in enriching the H₂ producing bacteria belonging to Clostridium sp. Species belonging to Propionibacterium, Bacteroides and Eubacterium, which were associated with H₂ consumption and reduced byproducts formation, were observed in addition to Clostridium sp. in unsparged control cultures.     

Bacterial community analyses by pyrosequencing in dark fermentative H2-producing reactor using organic wastes as a feedstock

Hydrogen(H₂)-producing bacterial community structures of the dark fermentation system in a batch reactor were investigated during 48 h by analyzing 16S rRNA gene sequences obtained from pyrosequencing. Organic wastes composed of food waste and sewage sludge were used as a feedstock. After heat treatment (90 °C for 20 min) of the feedstock, H₂ was naturally evolved under anaerobic mesophilic conditions, showing a H₂ yield of 2.26 mol H₂/mol hexose_added. The bacterial community structure of the initial inoculum (microbial community at the starting point (0 h)) combined with heat treated food waste and sewage sludge was mainly comprised of Proteobacteria and Bacteroidetes. After 6 h operation, the sequences that belong to other groups except Firmicutes decreased dramatically and were not observed at all in the latter samples. Clostridium spp., which were negligible in the inoculum, took over the main bacterial community by taking charge of H₂ production. Among the phylum Firmicutes, the sequences closely related with Clostridium sordellii ATCC 9714^T, Clostridium perfringens ATCC 13124^T, and Clostridium butyricum ATCC 19398^T became predominant in the time series within 48 h. Overall, the results showed how fast the Clostridium spp. overwhelmed the bacterial community in dark fermentative H₂ production conditions, where they were at a negligible amount at the start.     

Novel dark fermentation involving bioaugmentation with constructed bacterial consortium for enhanced biohydrogen production from pretreated sewage sludge

The present study summarizes the observations on various nutrient and seed formulation methods using sewage sludge that have been aimed at ameliorating the biohydrogen production potential. Pretreatment methods viz., acid/base treatment, heat treatment, sterilization, freezing–thawing, microwave, ultrasonication and chemical supplementation were attempted on sludge. It was observed that pretreatment was essential not only to reduce the needless, competitive microbial load but also to improve the nutrient solublization of sludge. Heat treatment at 121 °C for 20 min was found to be most effective in reducing the microbial load by 98% and hydrolyzing the organic fraction of sludge. However, this pretreatment alone was either not sufficient or inconsistent in developing a suitable microbial consortium for hydrogen production. Hydrogen yield was found to improve 1.5–4 times upon inoculation with H₂-producing microorganisms. A defined microbial consortium was developed consisting of three established bacteria viz., Enterobacter cloacae IIT-BT 08, Citrobacter freundii IIT-BT L139 and Bacillus coagulans IIT-BT S1. Following pretreatments soluble proteins and lipids (the major component of the sludge) were also found to be consumed besides carbohydrates. This laid out the concurrent proteolytic/lipolytic ability of the developed H₂-producing consortium. 1:1:1 v/v ratio of these bacteria in consortium was found to give the maximum yield of H₂ from sludge, 39.15 ml H₂/g COD_reduced. 15%v/v dilution and supplementation with 0.5%w/v cane molasses prior to heat treatment was found to further improve the yield to 41.23 ml H₂/g COD_reduced.     

Hydrogen bioproduction with anaerobic bacteria consortium from brewery wastewater

Biohydrogen production is a cheap and clean way to obtain hydrogen gas. In subtropical countries such as Brazil the average temperatures of 27 °C can favor the hydrogen producing bacteria growth. A mixed culture was obtained from a subtropical sludge treating brewery wastewater and anaerobic batch reactors were fed with glucose, sucrose, fructose and xylose in low concentrations (2.0, 5.0 and 10.0 g L⁻¹) at 37 °C, initial pH 5.5 and headspace with N₂ (99%) to maintain the anaerobic conditions. The inoculum was a subtropical granulated sludge from UASB (Upflow Anaerobic Sludge Blanket) reactor treating brewery wastewater. The higher H₂ yields were obtained in reactors operated with 2 and 5 g L⁻¹ of fructose and they were 1.5 mol H₂ mol⁻¹ of fructose and 1.3 mol H₂ mol⁻¹ of sucrose, respectively. The volatile fatty acids (VFA) generated at the end of operation were, predominantly, butyric and acetic acid, indicating the favoring of the metabolic route of hydrogen generation by the consortium of anaerobic bacteria from the brewery wastewater. Biomolecular analyses revealed the predominance of hydrogen producing bacteria from Firmicutes phylum distributed in the families Streptococcaceae, Veillonellaceae and uncultured bacteria. These results confirm future applications of subtropical sludges with agroindustrial wastewaters containing low concentrations of sugars on hydrogen generation.     

Kinetics and performance evaluation of microbial fuel cell supplied with dairy wastewater with simultaneous power generation

Due to the growing demand for energy in the present-day world, it is obligatory to look for alternative sources of renewable energy. The derivation of power from microbial fuel cells (MFCs) has developed at the vanguard of the alternative source of renewable energy through the concomitant treatment of wastewater. Hence, the process development of MFC is obligatory for creating a sustainable source of renewable energy through the treatment of wastewater. To that end, an attempt was taken in the present study for sustainable power generation from single chamber microbial fuel cell (SCMFC) using Pseudomonas aeruginosa-MTCC-7814. The experiments were carried out in a batch process for 15 days with real dairy wastewater (RDW) having initial chemical oxygen demand (COD) of 8000 mg/L. The open-circuit voltage (OCV) found after 72 h of batch operation was 658 mV, which was maximum within the batch operation. The columbic efficiency (CE) of the batch process was found to be 46.59%. The maximum specific growth rate (μ_max) of Pseudomonas aeruginosa-MTCC-7814 was found to be 0.432 day^?1 during batch operation. However, saturation constant (Ks) and inhibition coefficient (K_i) were calculated as 608.74 mg/L, and 6582 mg/L, respectively. The maximum current density (I_max) and saturation constant (K_c) predicted from batch kinetics study were 132 mA/m² and 321 mg/L, respectively, which has resemblance with the data obtained from experiments. The maximum current density and power density from experiments were found to be 161 mA/m² and 34.82 mW/m², respectively. Results showed that a higher power density and current density values were obtained from the present study as compared to the earlier reports that utilized wastewater as the substrate for the MFC. Thus, the study suggests that Pseudomonas aeruginosa, (MTCC-7814) can be used as a promising biocatalyst in MFC for sustainable power generation through the utilization of wastewater treatment.     

Hydrogen production from sludge of poultry slaughterhouse wastewater treatment plant pretreated with microwave

This study aims to produce hydrogen from sludge of poultry slaughterhouse wastewater treatment plant (5% total solid) by anaerobic batch fermentation with Enterobactor aerogenes or mixed cultures from hot spring sediment as the inoculums. Sludge was heated in microwave at 850 W for 3 min. Results indicated that a soluble chemical oxygen demand (sCOD) of pretreated sludge was higher than that of raw sludge. Pretreated sludge inoculated with E. aerogenes and supplemented with the Endo nutrient had a higher hydrogen yield (12.77 mL H₂/g tCOD) than the raw sludge (0.18 mL H₂/g tCOD). When considered the hydrogen yield, the optimum initial pH for hydrogen production from microwave pretreated sludge was 5.5 giving the maximum value of 12.77 mL H₂/g tCOD. However, when considered the hydrogen production rate (R_m), the optimum pH for hydrogen production would be 9.0 with the maximum R_m of 22.80 mL H₂/L sludge·h.     

Effect of pH control on biohythane production and microbial structure in an innovative multistage anaerobic hythane reactor (MAHR)

An innovative multistage anaerobic hythane reactor (MAHR) which combines an internal biofilm (M_H) and an external up-flow sludge blanket (M_M) was proposed to produce biohythane from wastewater. The effect of pH on its biohythane production and microbial diversity was performed. Results showed that the maximum hydrogen production rate (4.900 L/L/d) was achieved at a pH of 6.0, in comparison to a maximum methane production rate of 10.271 L/L/d at a pH of 6.5. In addition, a suitable hythane (H₂/(H₂+CH₄) of 16.06%) production can be achieved in M_H after the initial pH was adjusted from 7.0 to 6.5, and a relatively high methane yield (271.34 mL CH₄/gCOD) was obtained in M_M. Illumina Miseq sequencing results revealed that decreasing pH led to an increase of the acidogenesis families (Eubacteriaceae, Ruminococcaceae) in M_H and an increase of hydrogenotrophic methanogens (Methanobacteriaceae) in M_M. The Methanosaetaceae gradually occupied a major portion after a long period of recovery. This work demonstrated the unique advantages of MAHR for the biohythane production under optimal pH conditions.     

Optimization of high-solid waste activated sludge concentration for hydrogen production in microbial electrolysis cells and microbial community diversity analysis

To enhance hydrogen recovery from high-solid waste activated sludge (WAS), microbial electrolysis cells (MECs) were used as an efficient device. The effects of WAS concentrations were firstly investigated. Optimal concentration for hydrogen production was 7.6 g VSS/L. Maximum hydrogen yields reached to 4.66 ± 1.90 mg-H₂/g VSS and 11.42 ± 2.43 mg-H₂/g VSS for MECs fed with raw WAS (R-WAS) and alkaline-pretreated WAS (A-WAS) respectively, which was much higher than that obtained traditional anaerobic digestion. Moreover, no propionic acid accumulation was achieved at the optimal concentration. Effective sludge reduction was also achieved in MECs feeding with A-WAS. 52.9 ± 1.3% TCOD were removed in A-WAS MECs, meanwhile, protein degradation were 50.4 ± 0.8%. The 454 pyrosequencing analysis of 16S rRNA gene revealed the syntrophic interactions were existed between exoelectrogen Geobacter and fermentative bacteria Petrimonas, which apparently drove the efficient performance of MECs fed with WAS.     

Investigation of anaerobic digestion of Chlorella sp. and Micractinium sp. grown in high-nitrogen wastewater and their co-digestion with waste activated sludge

This study investigated two wildtype green algae, Micractinium sp. and Chlorella sp., for their growth in high nitrogen wastewater (mixture of sludge centrate and primary effluent wastewater) and subsequent anaerobic digestion under mesophilic conditions. Extraction and analysis of extracellular polymeric substances (EPS) in both algal species during cultivation showed that Micractinium generated larger quantity of EPS-proteins than Chlorella. Anaerobic digestion of harvested algae showed the opposite trend that Chlorella allowed a higher CH₄ yield on the volatile solids fed the digester (VS_fed) of 230 dm³ kg⁻¹ than Micractinium (209 dm³ kg⁻¹). These results suggested that different growth patterns of two types of algae, with different quantity of EPS expressed, affected anaerobic digestibility and biogas yield. Co-digestion of algae with waste activated sludge (WAS) improved the volatile solids reduction, hydrolysis efficiency as well as the biogas yields of algae.