High OLR Research Articles

A multistage biogas slurry reflux and spray anaerobic digestion reactor for high solid anaerobic digestion: Performance and application evaluation

In this study, a new vertical plug-flow continuous dry anaerobic digestion reactor equipped with a spray percolation system was designed for rice straw and cow manure in dry AD. The findings indicated that the methane yield was 290.63 ± 19.16 mL/g VS when the optimal spray time (9 times/d) was used in batch AD. In addition, the results of continuous experiments under optimal spray time conditions showed that the volumetric methane production rate of the system was 1.55 L/(L·d) when the organic loading rate was 20 g VS/(L·d). In addition, hydrolysis and acidification steps were enhanced. This study demonstrated the potential of the new reactor for stable operation of high OLR dry AD. Digestate is already used as a substitute for synthetic fertilizers precisely because of the environmental benefits associated with its agronomic use.

Co-Digestion and Mono-Digestion of Sewage Sludge and Steam-Pretreated Winter Wheat Straw in Continuous Stirred-Tank Reactors—Nutrient Composition and Process Performance

Wheat straw (WS) constitutes a considerable biomass resource and can be used to produce the energy carrier methane through anaerobic digestion. Due to the low contents of several nutrient elements and water in harvested WS, the use of sewage sludge (SS), consisting of primary sludge and waste-activated sludge, as a nutrient source in co-digestion with steam-pretreated wheat straw (PWS) was investigated theoretically and practically. WS was steam-pretreated, with acetic acid as the catalyst, at 190 °C for 10 min, ending with a rapid reduction in pressure. Process stability and specific methane production were studied for the mono-digestion and co-digestion of PWS and SS in continuous stirred-tank reactors for 208 days. The HRT was 22 days and the OLR 2.1 gVS L−1 d−1. In co-digestion, the OLR was increased to 2.8 gVS L−1 d−1 for one week. Nutrient elements were added to PWS mono-digestion at two different concentration levels. Co-digestion was stable, with a total concentration of short-chain fatty acids (SCFAs) at a safe level below 0.35 g L−1 at both OLRs. The higher OLR during co-digestion would require an increase in reactor volume of 14%, compared to the mono-digestion of SS, but would increase the annual production of methane by 26%. The specific methane production levels for PWS mono-digestion, SS mono-digestion, and co-digestion were 170, 320, and 260 mL g−1VS, respectively. Co-digestion did not result in a synergistic increase in the methane yield. SCFAs accumulated in the mono-digestion of PWS when using lower levels of nutrient supplements, and the concentrations fluctuated at higher nutrient levels. The main conclusion is that PWS and SS can be co-digested with long-term process stability, without the addition of chemicals other than water and acetic acid. The specific methane production for mono-digestion of PWS was relatively low. The effect of using higher concentrations of micronutrients in PWS mono-digestion should be evaluated in future studies.

PHA and EPS production from industrial wastewater by conventional activated sludge, membrane bioreactor and aerobic granular sludge technologies: A comprehensive comparison

The present study has focused on the mainstream integration of polyhydroxyalkanoate (PHA) production with industrial wastewater treatment by exploiting three different technologies all operating in sequencing batch reactors (SBR): conventional activated sludge (AS-SBR), membrane bioreactor (AS-MBR) and aerobic granular sludge (AGS). A full aerobic feast/famine strategy was adopted to obtain enrichment of biomass with PHA-storing bacteria. All the systems were operated at different organic loading (OLR) rate equal to 1-2-3 kgCOD/m3∙d in three respective experimental periods. The AS-MBR showed the better and stable carbon removal performance, whereas the effluent quality of the AS-SBR and AGS deteriorated at high OLR. Biomass enrichment with PHA-storing bacteria was successfully obtained in all the systems. The AS-MBR improved the PHA productivity with increasing OLR (max 35% w/w), whereas the AS-SBR reduced the PHA content (max 20% w/w) above an OLR threshold of 2 kgCOD/m3∙d. In contrast, in the AGS the increase of OLR resulted in a significant decrease in PHA productivity (max 14% w/w) and a concomitant increase of extracellular polymers (EPS) production (max 75% w/w). Results demonstrated that organic carbon was mainly driven towards the intracellular storage pathway in the AS-SBR (max yield 51%) and MBR (max yield 61%), whereas additional stressors in AGS (e.g., hydraulic selection pressure, shear forces) induced bacteria to channel the COD into extracellular storage compounds (max yield 50%) necessary to maintain the granule's structure. The results of the present study indicated that full-aerobic feast/famine strategy was more suitable for flocculent sludge-based technologies, although biofilm-like systems could open new scenarios for other biopolymers recovery (e.g., EPS). Moreover, the AS-MBR resulted the most suitable technology for the integration of PHA production in a mainstream industrial wastewater treatment plant, considering the greater process stability and the potential reclamation of the treated wastewater.

Polyhydroxyalkanoates production from a waste-derived feedstock driven by the reactor operating conditions: The role of biomass microbiome and its reactivation capacity

In the last years, the production of plastics at large-scale has been an issue of great concern due to their environmental and health impacts. Biobased and biodegradable plastics, such as polyhydroxyalkanoates (PHA), have emerged as a possible more ecological and sustainable alternative to those conventional plastics. PHA can be produced by mixed microbial cultures (MMC) from waste-based feedstocks. This work aimed to maximize the PHA production from fermented brewer's spent grain by selecting an efficient PHA-accumulating MMC, applying different organic loading rates (OLR, 45 or 60 CmmolFP/(L.d)) and sludge retention times (SRT, 4 or 2 days). Additionally, the biomass reactivation capacity after storage was evaluated.The global PHA productivity depends on the operating conditions, achieving its maximum (3.55 ± 0.8 gPHA/(L.d)) at the highest OLR and SRT tested. After storage, the global PHA productivity was similar to the one achieved before the starvation period.Depending on the operating conditions, the microbiome has its own bacterial composition signature containing various PHA-producers genera (e.g., Acidovorax, Amaricoccus, Brevundimonas, Leucobacter, Leadbetterella and Thauera) that persisted over time, albeit at different relative abundancies.A comprehensive overview of PHA production with data on system performance and microbiome is presented, which thereby can further contribute to the upscale of such valorisation processes.

Respirometric tests in a combined UASB-MBR system treating wastewater containing emerging contaminants at different OLRs and temperatures: Biokinetic analysis

This research focuses on the application of respirometric techniques to provide new insights into the biokinetic behaviour of bacterial species developed in an Upflow Anaerobic Sludge Blanked -UASB reactor combined with a membrane bioreactor -MBR, treating urban wastewater with emerging contaminants frequently found in this kind of effluents. The lab-scale pilot plant was operated at different metabolic and operational conditions by limiting the organic loading rate- OLR of the influent. In a first stage, the MBR was performed with suspended biomass, while in a second stage bio-supports were introduced to operate coexisting suspended and fixed biomass. From the results of the microscopic monitoring of sludge, it was concluded that the decrease in OLR resulted in a greater disintegration of the floc structure, more dispersed growth, and a low presence of inter-floccular bonds. However, no effect of toxicity or inhibition of microorganisms caused by the presence of emerging contaminants -ECs was determined. Kinetic modelling was carried out to study the behaviour of the system. The results showed a slowing down of biomass degradative capacity at low OLR stages and operating at low temperatures of mixed liquor. In addition, a decrease in oxygen consumption was observed with decreasing biodegradable substrate, resulting in lower degradation of organic matter. Mean values of specific oxygen uptake rate and heterotrophic biomass yield at low OLR were SOUR end = 1.49 and 1.15 mg O2· g MLVSS−1 h−1 and YH,MLSSV end = 0.48 and 0.28 mg MLVSS· mg COD−1substrate at stage 1 (suspended biomass) and stage 2 (suspended and supported biomass), respectively. From the analysis of the endogenous decomposition constant (kd), a higher cell lysis was determined operating with suspended biomass (kd = 0.03 d−1) in comparison to the operation coexisting suspended and supported biomass (kd = 0.01 d−1). Heterotrophic biomass yield values (YH, MLVSS = 0.48 ± 0.06, 0.40 ± 0.01 and 0.29 ± 0.01 mg MLVSS· mg COD−1substrate at high, medium and low OLR) showed lower sludge production at low OLR due to the influence of substrate limitation on cell growth.

Analysis of Large-Scale Environmental Features during Maximum Intensity of Tropical Cyclones Using Reanalysis Data

The present study investigates the variation in large-scale environments during the maximum intensity of tropical cyclones (TCs) formed in the Bay of Bengal. TC tracks are classified into four groups based on their direction of movement using the k-means clustering technique. Results from the pressure level and azimuthal-averaged radial-height wind fields near the vortex centre show weak deep layer wind shear (WS) and abundant moisture in all clusters. However, large-scale environmental differences in the northwest quadrant are identified with a contrasting combination of WS and humid environment between clusters. The composites of OLR are also analyzed during maximum intensities of TCs. Results show that anomalous high OLR in the west–northwest direction from the vortex centre, along with the low OLR around the vortex centre, signify the formation of a strong OLR dipole during TC peak intensity. Furthermore, OLR dipole metrics, such as magnitude, orientation, and distance, are observed by having mean of 235 Wm−2, 147, and 1782 km along with standard deviation of 14 Wm−2, 34°, and 492 km, respectively. The identified large-scale environmental fields from this study could provide valuable insights for predicting the intensity and movement of TCs.

Thermophilic anaerobic digestion of kitchen waste driven by microbial electrolysis cell (MEC): Digestion performances, anodic microorganisms’ distribution and current utilization efficiency

The aims of present study were to investigate the performances of kitchen waste thermophilic anaerobic digestion driven by microbial electrolysis cell (MEC), and to clarify the methanogenic metabolism pathways on the electrodes (especially on the anodic biofilm). The results showed that both 0.6 V and 1.0 V voltages supplementation could enhance methane yields and production rates, while efficient methanogenesis failed to be sustained after power outages under high organic loading rate (OLR, 4.22 gVS/L/day) condition. Voltages supplementation could also enhance VS removal efficiencies from 83.24–83.35% to 87.01–87.46%, and strengthened the hydrolysis and acidogenesis of dissolved organic matters (DOMs) on the outer layer of anodic biofilm. Voltages supplementation accelerated the β-oxidation of volatile organic acids (VFAs) on the inner layer of anodic biofilm and facilitated acetoclastic methanogenesis on the outer layer of anodic biofilm. The generated electrons on the anode were transferred to the cathode for producing hydrogen as a substrate of hydrogenotrophic methanogenesis, rather than directly generating methane by reducing carbon dioxide through direct interspecies electron transfer (DIET) pathway. On the anodic biofilm, the syntrophic relationship between Syntrophomonas and Methanosarcina was confirmed as the main contributor of methanogenesis. Analysis of current utilization efficiency proved that a little amount of energy input could lead several folds of current utilization efficiencies in return, especially under high OLRs condition, which was anticipated to be applied into practical engineering of kitchen waste thermophilic digestion for higher economic benefits.

Effect of organic load regulation on anaerobic digestion performance and microbial community of solar-assisted system of food waste

Abstract The semi-continuous digestion experiment of food waste was carried out based on a solar-assisted heat anaerobic digestion reactor. The effects of organic load regulation (OLR of 2.0, 4.0, 6.0 and 7.0 kg m−3 d−1 VS (volatile solid)) on methane production, physical and chemical parameters, and microbial community structure were studied. The results showed that 6.0 kg m−3 d−1 VS could achieve the optimal methane production as the anaerobic digestion limit OLR of kitchen waste. At this stage, the accumulation of organic acids in the reactor led to a great fluctuation of pH. Artificial alkali regulation could restore the stable operation of the reactor, but the reactor could not withstand the OLR shock of 7.0 kg m−3 d−1 VS. In addition, Qualcomm sequencing results showed that microorganisms showed high functional concentration and poor community richness under low OLR, and increasing OLR could promote microbial richness. At the same time, the Methanosaeta of acetic acid methanogens was relatively abundant in the low OLR stage, while the hydrogen trophic methanogenic bacteria Methanoregula and Methanospirillum showed high activity in the high OLR stage, but the excessive reproduction of acidogenic bacteria in the digestive system would affect the stability of the archaea community when the OLR was too high.

Assessment of an Integrated and Sustainable Multistage System for the Treatment of Poultry Slaughterhouse Wastewater.

This paper assesses the performance of an integrated multistage laboratory-scale plant, for the treatment of poultry slaughterhouse wastewater (PSW). The system was comprised of an eco-flush dosed bio-physico pre-treatment unit for fats, oil, and grease (FOG) hydrolysis prior to the PSW being fed to a down-flow expanded granular bed reactor (DEGBR), coupled to a membrane bioreactor (DEGBR-MBR). The system’s configuration strategy was developed to achieve optimal PSW treatment by introducing the enzymatic pre-treatment unit for the lipid-rich influent (PSW) in order to treat FOG including odour causing constituents such as H2S known to sour anaerobic digestion (AD) such that the PSW pollutant load is alleviated prior to AD treatment. This was conducted to aid the reduction in clogging and sludge washout in the DEGBR-MBR systems and to achieve the optimum reactor and membrane system performance. A performance for the treatment of PSW after lipid reduction was conducted through a qualitative analysis by assessing the pre- and post-pre-treatment units’ chemical oxygen demand (COD), total suspended solids (TSS), and FOG concentrations across all other units and, in particular, the membrane units. Furthermore, a similar set-up and operating conditions in a comparative study was also performed. The pre-treatment unit’s biodelipidation abilities were characterised by a mean FOG removal of 80% and the TSS and COD removal reached 38 and 56%, respectively. The final acquired removal results on the DEGBR, at an OLR of ~18–45 g COD/L.d, was 87, 93, and 90% for COD, TSS, and FOG, respectively. The total removal efficiency across the pre-treatment-DEGBR-MBR units was 99% for COD, TSS, and FOG. Even at a high OLR, the pre-treatment-DEGBR-MBR train seemed a robust treatment strategy and achieved the effluent quality set requirements for effluent discharge in most countries.

Elucidating the key factors in semicontinuous anaerobic digestion of urban biowaste: The crucial role of sludge addition in process stability, microbial community enrichment and methane production

Anaerobic digestion, a virtuous process to reduce and reuse biowaste to obtain renewable bioenergy, is often dramatically subject to process failure during long timescale operation. This study aimed to evaluate the process robustness and reliability by elucidating the composition of microbial populations and the link with process parameters under a wide range of different operating conditions in long-term semicontinuous reactors. Mesophilic semipilot digesters were fed with real urban biowaste, namely, food waste alone or food waste with activated sludge, to explore the impact of feedstock composition and organic loading rate (OLR: 0.8–3.5 kgVSfed m−3d−1) on volatile fatty acid (VFA) composition and pattern, biomethane production, and core microbiome dynamics. The major bacterial phyla were Bacteroidetes (basically more abundant when the feedstock was only food waste), followed by Chloroflexi and Firmicutes, while Euryarcheota hydrogenotrophic methanogens, mainly represented by members of the Methanomicrobiales family, prevailed in all systems. During monodigestion of food waste, however, independent of the OLR, methanogenic conversion of fermentative end-products decreased progressively after 1 HRT. In particular, the observed propionate and butyrate accumulations seemed to derive from thermodynamic limitations due to the increase in hydrogen levels, indicative of progressively lower H2 consumption rates. However, the induced process recovery assured a large degradation of fatty acids with higher carbon chain lengths together with methane production, suggesting the upswing of hydrogenotrophic methanogen activity emerging after stressful conditions. The addition of a minimal amount of sludge boosted the methane production rates (up to 0.29 ± 0.1 Nm3CH4 kg−1VSfed) along with excellent process stability, also at a high OLR, creating a robust methanogen community shaped by high biodiversity. Methanospirillum and Candidatus Methanofastidiosum, strictly related to the codigestion systems, have a large H2 consumption capacity, thus preventing thermodynamic bottlenecks and process failure.

Wastewater treatment performance and microbial community of anode electrodes of membrane and membrane-less MFCs under effect of sunlight

This study investigated the anodic microbial community and treatment efficiency of two MFC systems, membrane MFC (M-MFC) and membrane-less MFCs (ML-MFC) operated in the open environment under effect of sunlight. Both MFCs were inoculated with anaerobic sludge, operated under continuous mode in the open environment effected by sunlight, treated synthetic wastewater with step-wise increasing of organic loading rates (ORLs) of 3.0; 3.5; 4.0; and 4.5 g COD/L·day. The COD removal and the power generation were continuously monitored. COD removal efficiency of M-MFC for each OLR was 34.7 ± 23.7%, 76.7 ± 6.7%, 71.9 ± 0.7%, and 67.9 ± 2.8%, respectively. For the ML-MFC, COD removal efficiency was 54.3 ± 13.5%, 73 ± 1.7%, 73.7 ± 1.6%, and 68.1 ± 4%, respectively. Power density of ML-MFC under all ORLs was much higher than that of the M-MFC. Results from Illumina high throughput sequencing of 16S rRNA genes showed that there was difference anodic microbial community structure between M-MFC and ML-MFC. The microbial community in the ML-MFC was more diverse than in the M-MFC. This variation attributed to the differences in the design as well as the effect of sunlight to which these systems exposed to. M-MFC and ML-MFC shared the same dominant bacterial phyla; Proteobacteria and Firmicutes, and Synergistetes, with the most abundant bacterial genus in both MFCs belonging to Rhodopseudomonas. Sunlight has found promote the growth of the Rhodopseudomonas genus. The efficiency of the MFCs was reduced at the high OLR and longtime operated under open environment.

Kinetics and performance study of ultrasonic-assisted membrane anaerobic system using Monod Model for Palm Oil Mill Effluent (POME) treatment

The discharge of Palm Oil Mill Effluent (POME) to river or sewage has caused serious environmental problems for the past several decades. This has prompted many researchers to find alternative technologies such as the use of an ultrasonic-assisted membrane anaerobic system, also known as UMAS. However, further use of UMAS in treating POME tends to create blockage on the membrane surface, which is commonly known as membrane fouling. In this study, kinetic parameters of POME samples which contributed to the fouling were investigated, namely; the biomass growth rate, μ max and substrate utilization rate, K s . Two different sources of POME samples were taken from namely; a final discharge pond at Felda Sungai Tengi, Selangor and decanter processing units at Felda Jengka, Pahang. The POME samples were treated by UMAS in a 26-Litre laboratory reactor which operated 5 ​h per day for a HRT of 7 days so as to observe their performance in terms of percentage COD removal and CH 4 production. Performance results revealed that maximum COD removal efficiencies were 82.75% and 94.43% for the final discharge pond and decanter processing unit samples respectively. All these data were collected and curve fitting methods were then used to construct appropriate profiles for μ max and K s following a Monod model. It was found that the high OLR sample (decanter) apparently yielded better efficiency of POME treatment (i.e. calculated μ max of 0.327 day −1 , K s of 0.361 ​g COD/g VSS. d, and volume of CH 4 gas produced at 25 ​m 3 ) compared to that of low OLR sample from ponds (i.e. calculated μ max of 0.237 day −1 , K s of 0.1674 ​g COD/VSS. d, and volume of CH 4 gas produced at 9 ​m 3 ). In conclusion, it shows that UMAS is a promising treatment to treat POME in which its calculated kinetic coefficients of μ max and K s are similar to the theoretical values when Monod Model is employed in this study. • COD removal efficiencies were achieved at 82.75% and 94.43% for the pond and decanter samples, respectively. • Calculated values for µ max were 0.237 day -1 and 0.327 day -1 for the pond and decanter samples, respectively. • Calculated K s value for the decanter sample was at 0.361 g COD/g VSS. d. • Calculated K s value for the pond sample was at 0.167 g COD/ g VSS. d. • At 7 days HRT, CH 4 gas produced was higher (25 m 3 ) from the decanter samplecompared to 9 m 3 only from the pond sample.

Carbamazepine removal from low-strength municipal wastewater using a combined UASB-MBR treatment system.

An Upflow Anaerobic Sludge Blanket reactor combined with a two-stage membrane bioreactor were operated for 193 days in order to evaluate the biological removal of carbamazepine (CBZ) from low-strength municipal wastewater. The system worked in three different organic load stages (0.7 ± 0.1 kg COD·m-3·d-1, 0.4 ± 0.1 kg COD·m-3·d-1 and 0.1 ± 0.0 kg COD·m-3·d-1) to assess the impact of the influent OLR on operational parameters such as anaerobic and aerobic sludge retention time (SRT), acidity, volatile fatty acids (VFAs), biomass activity or biogas production. The highest carbamazepine removals were achieved during the anaerobic stage (UASB reactor), reaching averages of 48.9%, 48.0% and 38.2% operating at high, medium and low OLR, respectively. The aerobic treatment (MBR) served as post-treatment, improving the removals, and the global UASB-MBR system reached averages of 70.0%, 59.6% and 49.8% when the influent was at medium and low OLR, respectively. The results demonstrate the potential of combined biological systems on the removal of recalcitrant pharmaceuticals.

Roles of colloidal particles and soluble biopolymers in long-term performance and fouling behaviors of submerged anaerobic membrane bioreactor treating methanolic wastewater

Abstract Anaerobic membrane bioreactor (AnMBR) has been applied as a promising technology for treating a variety of industrial wastewaters. Nevertheless, the potential of AnMBR for methanolic wastewater treatment is still not well recognized. In this study, a lab-scale AnMBR fed with low-strength methanolic wastewater was operated for 166 days with stepwise decreased HRT, and the roles of colloidal particles and soluble biopolymers in membrane fouling behaviors were elucidated comprehensively. The results showed that AnMBR showed the desirable performance and process stability with total chemical oxygen demand removal of 89.8 ± 1.1% and the highest methane production rate of 5.49 L/L-reactor/d at organic loading rate of 20.00 g-COD/L-reactor/d and hydraulic retention time of 18 h. The serious membrane fouling was observed after a period of operation at low HRT or high OLR due to the production of colloidal particles and the liberation of soluble biopolymers. Decreased particle size, and increased adhesion forces of gel-like flocs caused by the secretion of hydrophobic protein-bearing biopolymers accelerated the deposition of foulants and the formation of cake layer, inducing the easily mitigated membrane fouling. Further observations proved that the main bioconversion pathway of methanolic wastewater to biomethane was methylotrophic methanogenesis, followed by acetotrophic/hydrogenotrophic processes. Collectively, although the membrane fouling cannot be eliminated, this research confirmed the technical feasibility of AnMBR for methanolic wastewater treatment in real-world applications.

Anaerobic co-digestion of corn stover and chicken manure using continuous stirred tank reactor: The effect of biochar addition and urea pretreatment

The performance of biochar mediated anaerobic co-digestion (co-AD) of corn stover (CS) and chicken manure (CM) using continuous stirred tank reactor (CSTR) was studied. Results showed that urea pretreated CS (UPCS) and biochar addition in anaerobic digestion (AD) system can improve co-AD. The effect of urea pretreatment is similar to that of biochar addition, and their synergistic effect was apparent under medium and high OLR conditions. When the OLR was 4.2 and 6.3 g VS/L/d, the biochar mediated UPCS/CM co-AD operated stably with the VMP of 2.160 and 1.616 L/L/d, and VMP of the biochar mediated UPCS /CM were 32.8%–89.6% and 27.8%–96.4% higher than other reactors, respectively. The results reveal that urea pretreatment and biochar addition promoted AD process through strengthening the buffer capacity system established by ammonia nitrogen and volatile fatty acids and improving the degradation of lignocellulosic biomass.

Functional selection of bacteria in an activated sludge reactor for application in saline wastewater treatment in Kerkennah, Tunisia

Domestic wastewater entering the wastewater treatment plant (WWTP) of Kerkennah (Tunisia) contains high organic load and high salinity. The biological treatment of these influents with conventional microorganisms has proven to be not very effective, which might be improved by functionally selected halotolerant/halophilic heterotrophic bacteria. Therefore, a laboratory-scaled activated sludge reactor (ASR) was used for a continuous treatment of this wastewater. The performance of the ASR, inoculated with a mixed culture of active biomass gradually acclimated to the wastewater, was evaluated in terms of carbonaceous pollutant removal efficiency. Experiments were conducted at different organic loading rates (OLRs, varying from 250 to 1200 mg chemical oxygen demand (COD)/l.d). The descriptive analysis showed that the removal efficiency (r) of the ASR was high, peaking at 95% for CODr in medium OLRs, and up to 99% for Biological oxygen demand (BODr) and total suspended solids for high OLRs and salinity. The overall removal efficiency was improved by 1/3th or more compared to the WWTP by these selected and acclimated bacteria. The different observations were combined in an innovative statistical design of Hierarchical clustering. This method improves on traditional approaches by allowing flexibility in understanding the complex variations within the WWTP and the ASR. The identification of the bacterial biomass responsible for high BODr in the ASR by conventional microbiology demonstrated the dominance of Proteus mirabilis and Aeromonas hydrophila. The 16S rRNA gene gave a more accurate identification, indicating a great bacterial diversity and the possibility of a new species.

Effect of operating parameter on the anaerobic digestion oil palm mesocarp fibre with cattle manure for biogas production

Anaerobic digestion is a complex biological process resulting in the conversion of biodegradable organic matter into biogas and mineralized material. Anaerobic digestion involves the breakdown of biomass by a concerted action of a wide range of microorganisms in the absence of oxygen. The biological pre-treatment was used to reduce the lignocellulose content of substrate. Laboratory experiment was carried out in single stage 10 L bioreactors. The reactors were named R1, to R10 at different mixture conditions with organic loading of 1.62 and 2.11 g VS at HRT of 10 days. The result was stable at the initial stage, within the first 10 days was high and was attributed to the consumption of easily degradable COD. These indicate that there is stable COD removal efficiency for the anaerobic digestion of treated OPMF with CM and seeded with POME. The results showed the level of COD removal efficiency was observed and upon the steady state of the reaction. In this experiment, the results indicate that chemical oxygen demand (COD) reduction in reactor R1 shows the best result of the average removal efficiency value of 37.9 %. Although, ambient temperature was adopted, it still shows a high COD removal efficiency in R1 and may be associated to a more stable reaction. This indicated that pre-treated OPMF produced a better COD removal efficiency than the untreated OPMF. The removal efficiency started with 18 % and continued to increase to 38 %. The removal efficiency became relative stable until day 30 which give the highest percentage removal of 45 % which was achieved with a high OLR (2.11 kg VS L−1 d−1). The reductions continued in the same trend until day 20 and remained stable till the end of the experiment. This indicates that the available microorganisms have been exulted by day 20 and this corresponds to a drop to the rate of biogas production. Operating parameters considered in this study have an influence on the rate of biogas produced during anaerobic digestion. The results show that COD, do influence the rate of biogas production.

Interannual Variability of Rainfall over the West Africa Sahel

Interannual variability of the precipitation over West Africa Sahel is analyzed based on 32 years (1979-2010) from monthly and daily database of the Global Precipitation Climatology Project (GPCP). In this region, we found that there is a link between the West Africa Monsoon (WAM) and the daily means of the precipitation in the summer, unseasonal rains can occur in the transition seasons and even in the heart of the dry season. Rainfall is the most important element for agro-pastoral activities in this region. The 850-hPa wind and wind divergence structure show a maximum convection over Mountain region (Fouta-Djalon and Mont-Cameroon) which corresponds to the high precipitation and OLR observed in these regions. The trend and empirical orthogonal function (EOF) of the precipitation are presented, including the mid-July variability of the precipitation. The dominant EOF of GPCP precipitation accounts for around 25.3% of the variance with slightly large amplitude in the north while relatively small in the equatorial band respectively. The second and third EOF which accounts for 20.5% and 14%, describes a longitudinal contrast with a zonal gradient.

Effect of a side-stream voltage supplied by sludge recirculation to an anaerobic digestion reactor

This study showed that side stream voltage supplied by sludge recirculation from an auxiliary bio-electrochemical anaerobic digestion (ABEAD) reactor appears to have a similar effect as main stream voltage supply to an anaerobic digestion (AD) reactor. The increased sludge recirculation rate enhanced the operation stability at a high OLR. H2-producing bacterial community was improved in bio-electrochemical anaerobic digestion (BEAD) and ABEAD reactors and was increased with increase in sludge recirculation rate. Despite the dominance of hydrogenotrophic methanogens in all reactors, high operational performances of BEAD and ABEAD reactors supports the results of H2-producing bacteria increase in those reactors. The ABEAD reactors having 1/7 of the capacity of the main AD reactor showed possibility of integration of BEAD technology into new and existing facilities economically. The findings of this study would provide useful information for approaching the commercialization of BEAD and suggest direction of further research for practical applications.

Process analysis and optimization of single stage flexible fibre biofilm reactor treating milk processing industrial wastewater using response surface methodology (RSM)

Milk processing industries consume significant volumes of sustainable water during processing and operating steps to meet hygienic requirements. Therefore, such industries are recognized as a potential source for producing large volume of contaminated water which generally contains biodegradable matters, and are subsequently suitable to be biologically treated. Based on this, many researchers have been moving towards milk processing wastewater (MPW) treatment via biological approaches. In present study, the performance of a single stage flexible fibre biofilm reactor (SS-FFBR) in mitigation of organic loading of the MPW was assessed. The performance of SS-FFBR in terms of the biological treatment was statistically modelled and analysed in terms of HRT and CODin by employing response surface methodology (RSM). From the results, it is clear increase in HRT and decrease in the CODin led to incrementing the COD removal percentage. In addition, a significant mutual interaction occurs between the variables and other responses. The optimum removal was reported at an HRT of 8h and CODin of 3922mg/L corresponded to high OLR of 11.67kgCOD/m3d. The experimental results were in good agreement with model prediction.