A mathematical approach to predict the solids concentration in anaerobic membrane bioreactos (AnMBR): Evaluation of the volatile solids solubilization.

Anaerobic Membrane Bioreactors (AnMBR) are gaining attention as a suitable approach for sustainable low-strength wastewater treatment, as they bring together the advantages of both anaerobic treatments and membrane bioreactors. However, increasing the sludge retention time (SRT) necessary to favor hydrolysis increases the suspended solids concentration potentially leading to decreased permeate flux. Therefore, the availability of a mathematical approach to predict the solids concentration within an AnMBR can be very useful. In this work, a mathematical model describing the volatile solids concentration within the reactor as a function of the operating parameters and the influent characteristics is developed. The solubilization of organic particulates was clearly influenced by temperature and the SRT, whereas the hydraulic retention time influence was negligible. Furthermore, the activation energy value of about 20 kJ mol-1 confirms the idea that diffusion of hydrolytic enzymes from the bulk solution to the particle surface is the rate-limiting step of hydrolysis.

Acclimatised rumen culture for raw microalgae conversion into biogas: Linking microbial community structure and operational parameters in anaerobic membrane bioreactors (AnMBR).

Ruminal fluid was inoculated in an Anaerobic Membrane Reactor (AnMBR) to produce biogas from raw Scenedesmus. This work explores the microbial ecology of the system during stable operation at different solids retention times (SRT). The 16S rRNA amplicon analysis revealed that the acclimatised community was mainly composed of Anaerolineaceae, Spirochaetaceae, Lentimicrobiaceae and Cloacimonetes fermentative and hydrolytic members. During the highest biodegradability achieved in the AnMBR (62%) the dominant microorganisms were Fervidobacterium and Methanosaeta. Different microbial community clusters were observed at different SRT conditions. Interestingly, syntrophic bacteria Gelria and Smithella were enhanced after increasing 2-fold the organic loading rate, suggesting their importance in continuous systems producing biogas from raw microalgae.

Assessment of cross-flow filtration as microalgae harvesting technique prior to anaerobic digestion: Evaluation of biomass integrity and energy demand.

In the present study, the effect of cross-flow filtration (CFF) on the overall valorization of Chlorella spp. microalgae as biogas was assessed. The effect of CFF on microalgae cell integrity was quantified in terms of viability which was correlated with the anaerobic biodegradability. The viability dropped as the biomass concentration increased, whereas anaerobic biodegradability increased linearly with the viability reduction. It was hypothesized that a stress-induced release and further accumulation of organic polymers during CFF increased the flux resistance which promoted harsher shear-stress conditions. Furthermore, the volume reduction as the concentration increased entailed an increase in the specific energy supply to the biomass. The energy demand was positive in the whole range of concentrations studied, yielding an overall energy efficiency as high as 22.9% for the highest concentration studied. Specifically, heat requirements were lower than electricity requirements only when the biomass concentrations exceeded 10 g COD·L-1.

Enrichment of AOB and NOB Population by Applying a BABE Reactor in an Activated Sludge Pilot Plant.

This paper deals with the effect of a bioaugmentation batch enhanced (BABE) reactor implementation in a biological nutrient removal pilot plant on the populations of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). The results of fluorescence in situ hybridization (FISH) technique showed that AOB and NOB populations were significantly enhanced, from 4 to 8% and from 2 to 9%, respectively, as a result of the BABE reactor implementation. Regarding AOB, the percentage of Nitrosomonas oligotropha was mainly increased (3 to 6%). Regarding NOB, Nitrospirae spp was greatly enhanced (1 to 7%). Both species are considered K-strategist (high affinity to the substrate, low maximum growth rates) and they usually predominate in reactors with low ammonium and nitrite concentrations, respectively.

Impact of temperature on feed-flow characteristics and filtration performance of an upflow anaerobic sludge blanket coupled ultrafiltration membrane treating municipal wastewater.

The objective of this study was to assess the operational feasibility of an anaerobic membrane bioreactor (AnMBR), consisting of an upflow anaerobic sludge blanket (UASB) reactor coupled to an ultrafiltration membrane unit, at two operational temperatures (25°C and 15°C) for the treatment of municipal wastewater. The results showed that membrane fouling at 15°C was more severe than that at 25°C. Higher chemical oxygen demand (COD) and soluble microbial products (SMP) concentrations, lower mean particle diameter, and higher turbidity in the UASB effluent at lower temperature aggravated membrane fouling compared to the 25°C operation. However, the overall AnMBR treatment performance was not significantly affected by temperature, which was attributed to the physical membrane barrier. Cake resistance was found responsible for over 40% of the total fouling in both cases. However, an increase was observed in the contribution of pore blocking resistance at 15°C related to the larger amount of fine particles in the UASB effluent compared to 25°C. Based on the overall results, it is concluded that an AnMBR, consisting of a UASB coupled membrane unit, is not found technically feasible for the treatment of municipal wastewater at 15°C, considering the rapid deterioration of the filtration performance.