Integrated anaerobic and algal bioreactors: A promising conceptual alternative approach for conventional sewage treatment

Multi-bioinspired hierarchical integrated hydrogel for passive fog harvesting and solar-driven seawater desalination

In recent years, with the outbreak and epidemic of the novel coronavirus in the world, how to obtain clean water from the limited resources has become an urgent issue of concern to all mankind. Atmospheric water harvesting technology and solar-driven interfacial evaporation technology have shown great potential in seeking clean and sustainable water resources. Here, inspired by a variety of organisms in nature, a multi-functional hydrogel matrix composed of polyvinyl alcohol (PVA), sodium alginate (SA) cross-linked by borax as well as doped with zeolitic imidazolate framework material 67 (ZIF-67) and graphene owning macro/micro/nano hierarchical structure has successfully fabricated for producing clean water. The hydrogel not only can reach the average water harvesting ratio up to 22.44 g g-1 under the condition of fog flow after 5 h, but also be capable of desorbing the harvested water with water release efficiency of 1.67 kg m-2 h-1 under 1 sun. In addition to excellent performance in passive fog harvesting, the evaporation rate over 1.89 kg m-2 h-1 is attained under 1 sun on natural seawater during long-term. This hydrogel indicates its potential in producing clean water resources in multiple scenarios in different dry or wet states, and which holds great promise for flexible electronic materials and sustainable sewage or wastewater treatment applications.

Characterisation and perspectives of energetic use of dissolved gas recovered from anaerobic effluent with membrane contactor

Biogas is a source of renewable energy, and its production and use has been validated in anaerobic-based sewage treatment plants (STPs). However, in these systems, a large amount of methane is lost as dissolved methane (D-CH₄) in the liquid effluent. In this study, the characteristics and potential energetic uses of the gas recovered during the desorption of D-CH₄ from anaerobic effluents with hollow fibre membrane contactors were investigated. A pilot-scale experiment was performed using sewage and two types of membrane contactors. The recovered gas contained considerable amounts of CH₄, CO₂, H₂S, N₂, and O₂; therefore, a gas upgrade is required prior to its use as a biofuel. The recovery process should be energetically self-sustainable, and induce a considerable decrease in the STP carbon footprint. Recovering D-CH₄ with membrane contactors could increase the energetic potential of anaerobic-based STPs up to 50 % and allow for more sustainable systems.

Two-phase (acidogenic-methanogenic) anaerobic fixed bed biofilm reactor enhances the biological domestic sewage treatment: Perspectives for recovering bioenergy and value-added by-products

The organic matter bioconversion into methane during anaerobic digestion (AD) comprises different steps, the acidogenic and methanogenic phases being clearly distinct in terms of metabolic activities. In this work, new configurations of anaerobic fixed bed biofilm reactors (AFBBR) were operated under conventional methanogenic conditions (single phase - SP-AFBBR, M₁R), and in a sequential two-phase system, acidogenic reactor followed by methanogenic reactor (TP-AFBBR, AcR + M₂R), in order to verify the impact of the AD phase separation on the overall system performance in operational, kinetics and microbiological aspects. The results indicated that feeding the methanogenic reactor with the acidogenic effluent stream provided a shorter operating start-up period (11 and 32 days for SP and TP-AFBBR, respectively), a greater alkalinity generation (0.14 and 0.41 g-CaCO₃·g-COD_removed^-1 for M₁R and M₂R, respectively), and the optimization of biomethane production (methane yield of 95 and 154 N-mLCH₄·g-COD_removed^-1 for M₁R and M₂R, respectively). The COD removal kinetics was also favored in the TP-AFBBR (k_1-COD = 1.4 and 2.9 h^-1 for M₁R and M₂R, respectively), since the soluble fermentation products were readily bioavailable to the biomass in the reactor. Hydrogenotrophic methanogenesis was the predominant pathway in the M₂R, while the Methanosaeta-driven acetoclastic pathway predominated in the M₁R. The greater diversity of Bacteria and Archaea in M₂R denotes a better balance between the species that degrade volatile organic acids from AcR (i.e. Syntrophorhabdus, Syntrophus and Syntrophobacter) and the hydrogenotrophic methanogens (Methanoregula, Methanolinea and Methanospirillum) that consume the biodegradation products. The estimated bioenergy generation potential (range of 0.39-0.64 kWh·m^-3-sewage considering the COD removed) for full-scale TP-sewage treatment plants evidences the feasibility of energetic recovery in the domestic sewage anaerobic treatment.