Relationship between the synergistic/antagonistic effect of anaerobic co-digestion and organic loading

© 2017 Results from this study reveal a notable relationship between the synergistic/antagonistic performance of sewage sludge – food waste anaerobic co-digestion (AcoD) and organic loading. At the same sewage sludge content, biomethane potential assays show an increasing specific methane yield as the content of food waste increased to the optimum organic loading of 15 kg VS/m3. Under these conditions, the specific methane yields experimentally measured in this study were considerably higher than those calculated by adding the specific methane individual co-substrates during mono-digestion. On the other hand, at above the optimum organic loading value, the antagonistic effect (i.e. lower specific methane yield compared to mono-digestion) was observed. The relationship between synergistic performance of AcoD and organic loading was also evidenced in the removal of volatile solids as well as chemical oxygen demand. Further analysis of the intermediate products show that methanogenesis was the rate limiting step during AcoD at a high organic loading value. As the organic loading increased, the digestion lag phase increased and the hydrolysis rate decreased

Current status and perspectives on anaerobic co-digestion and associated downstream processes

© The Royal Society of Chemistry. Anaerobic co-digestion (AcoD) has the potential to utilise spare digestion capacity at existing wastewater treatment plants to simultaneously enhance biogas production by digesting organic rich industrial waste and achieve sustainable organic waste management. While the benefits of AcoD regarding biogas production and waste management are well established, the introduction of a new organic waste (i.e. co-substrate) with different chemical composition compared to residential sewage sludge is expected to impact on not only the anaerobic digestion process itself but also downstream processing of biogas and digestate. This work critically evaluates the potential impact (both positive and negative) of co-digestion on key downstream processes in the context of AcoD of sewage sludge and organic waste. AcoD can potentially lead to significant changes in biogas quality, digestate dewaterability, biosolids odour and the nutrient balance within the overall wastewater treatment process. The literature reviewed here suggests that effective management of these impacts can enhance the economic and environmental benefits of AcoD. Potential techniques to manage the impact of AcoD on downstream processing include co-substrate selection to minimise sulphur content, co-substrate pretreatment to improve dewaterability, process optimisation to minimize downstream impacts, biological desulphurisation of biogas, and side stream nutrient recovery. These techniques have been investigated and in some cases successfully applied for conventional anaerobic digestion. Nevertheless, further research is needed to adapt them for AcoD. In particular, the issue of nutrient accumulation due to AcoD can be seen as an opportunity to utilise recently commercialised technologies (e.g. Phosnix and Ostara) and currently emerging processes (e.g. forward osmosis and electrodialysis) for phosphorus recovery from food waste and wastewater

Anaerobic digestion of soft drink beverage waste and sewage sludge

© 2018 Soft drink beverage waste (BW) was evaluated as a potential substrate for anaerobic co-digestion with sewage sludge to increase biogas production. Results from this study show that the increase in biogas production is proportional to the increase in organic loading rate (OLR) rate due to BW addition. The OLR increase of 86 and 171% corresponding to 10 and 20% BW by volume in the feed resulted in 89 and 191% increase in biogas production, respectively. Under a stable condition, anaerobic co-digestion with BW did not lead to any significant impact on digestate quality (in terms of COD removal and biosolids odour) and biogas composition. The results suggest that existing nutrients in sewage sludge can support an increase in OLR by about 2 kg COD/m3/d from a carbon rich substrate such as soft drink BW without inhibition or excessive impact on subsequent handling of the digestate

Anaerobic co-digestion: A critical review of mathematical modelling for performance optimization

© 2016 Anaerobic co-digestion (AcoD) is a pragmatic approach to simultaneously manage organic wastes and produce renewable energy. This review demonstrates the need for improving AcoD modelling capacities to simulate the complex physicochemical and biochemical processes. Compared to mono-digestion, AcoD is more susceptible to process instability, as it operates at a higher organic loading and significant variation in substrate composition. Data corroborated here reveal that it is essential to model the transient variation in pH and inhibitory intermediates (e.g. ammonia and organic acids) for AcoD optimization. Mechanistic models (based on the ADM1 framework) have become the norm for AcoD modelling. However, key features in current AcoD models, especially relationships between system performance and co-substrates’ properties, organic loading, and inhibition mechanisms, remain underdeveloped. It is also necessary to predict biogas quantity and composition as well as biosolids quality by considering the conversion and distribution of sulfur, phosphorus, and nitrogen during AcoD

Thin-film composite forward osmosis membranes functionalized with graphene oxide–silver nanocomposites for biofouling control

© 2016 Elsevier B.V. Innovative approaches to prevent bacterial attachment and biofilm growth on membranes are critically needed to avoid decreasing membrane performance due to biofouling. In this study, we propose the fabrication of anti-biofouling thin-film composite membranes functionalized with graphene oxide–silver nanocomposites. In our membrane modification strategy, carboxyl groups on the graphene oxide–silver nanosheets are covalently bonded to carboxyl groups on the surface of thin-film composite membranes via a crosslinking reaction. Further characterization, such as scanning electron microscopy and Raman spectroscopy, revealed the immobilization of graphene oxide–silver nanocomposites on the membrane surface. Graphene oxide–silver modified membranes exhibited an 80% inactivation rate against attached Pseudomonas aeruginosa cells. In addition to a static antimicrobial assay, our study also provided insights on the anti-biofouling property of forward osmosis membranes during dynamic operation in a cross-flow test cell. Functionalization with graphene oxide–silver nanocomposites resulted in a promising anti-biofouling property without sacrificing the membrane intrinsic transport properties. Our results demonstrated that the use of graphene oxide–silver nanocomposites is a feasible and attractive approach for the development of anti-biofouling thin-film composite membranes

Osmotic versus conventional membrane bioreactors integrated with reverse osmosis for water reuse: Biological stability, membrane fouling, and contaminant removal

© 2016 This study systematically compares the performance of osmotic membrane bioreactor – reverse osmosis (OMBR-RO) and conventional membrane bioreactor – reverse osmosis (MBR-RO) for advanced wastewater treatment and water reuse. Both systems achieved effective removal of bulk organic matter and nutrients, and almost complete removal of all 31 trace organic contaminants investigated. They both could produce high quality water suitable for recycling applications. During OMBR-RO operation, salinity build-up in the bioreactor reduced the water flux and negatively impacted the system biological treatment by altering biomass characteristics and microbial community structure. In addition, the elevated salinity also increased soluble microbial products and extracellular polymeric substances in the mixed liquor, which induced fouling of the forward osmosis (FO) membrane. Nevertheless, microbial analysis indicated that salinity stress resulted in the development of halotolerant bacteria, consequently sustaining biodegradation in the OMBR system. By contrast, biological performance was relatively stable throughout conventional MBR-RO operation. Compared to conventional MBR-RO, the FO process effectively prevented foulants from permeating into the draw solution, thereby significantly reducing fouling of the downstream RO membrane in OMBR-RO operation. Accumulation of organic matter, including humic- and protein-like substances, as well as inorganic salts in the MBR effluent resulted in severe RO membrane fouling in conventional MBR-RO operation

Biomimetic aquaporin membranes for osmotic membrane bioreactors: Membrane performance and contaminant removal

© 2017 Elsevier Ltd In this study, we investigated the performance of an osmotic membrane bioreactor (OMBR) enabled by a novel biomimetic aquaporin forward osmosis (FO) membrane. Membrane performance and removal of 30 trace organic contaminants (TrOCs) were examined. Results show that the aquaporin FO membrane had better transport properties in comparison with conventional cellulose triacetate and polyamide thin-film composite FO membranes. In particular, the aquaporin FO membrane exhibited much lower salt permeability and thus smaller reverse salt flux, resulting in a less severe salinity build-up in the bioreactor during OMBR operation. During OMBR operation, the aquaporin FO membrane well complemented biological treatment for stable and excellent contaminant removal. All 30 TrOCs selected here were removed by over 85% regardless of their diverse properties. Such high and stable contaminant removal over OMBR operation also indicates the stability and compatibility of the aquaporin FO membrane in combination with activated sludge treatment

The fate of trace organic contaminants during anaerobic digestion of primary sludge: A pilot scale study

© 2018 A pilot-scale study was conducted to investigate the fate of trace organic contaminants (TrOCs) during anaerobic digestion of primary sludge. Of the 44 TrOCs monitored, 24 were detected in all primary sludge samples. Phase distribution of TrOCs was correlated well with their hydrophobicity (>67% mass in the solid phase when LogD > 1.5). The pilot-scale anaerobic digester achieved a steady performance with a specific methane yield of 0.39–0.92 L/gVSremoved and methane composition of 63–65% despite considerable variation in the primary sludge. The fate of TrOCs in the aqueous and solid phases was governed by their physicochemical properties. Biotransformation was significant (>83%) for five TrOCs with logD 1.5 were poorly removed under anaerobic conditions. Sorption onto the solid phase appears to impede the biodegradation of these TrOCs

Evolution of cooperation driven by zealots

Recent experimental results with humans involved in social dilemma games suggest that cooperation may be a contagious phenomenon and that the selection pressure operating on evolutionary dynamics (i.e., mimicry) is relatively weak. I propose an evolutionary dynamics model that links these experimental findings and evolution of cooperation. By assuming a small fraction of (imperfect) zealous cooperators, I show that a large fraction of cooperation emerges in evolutionary dynamics of social dilemma games. Even if defection is more lucrative than cooperation for most individuals, they often mimic cooperation of fellows unless the selection pressure is very strong. Then, zealous cooperators can transform the population to be even fully cooperative under standard evolutionary dynamics.Comment: 5 figure

Nonlinear vortex light beams supported and stabilized by dissipation

We describe nonlinear Bessel vortex beams as localized and stationary solutions with embedded vorticity to the nonlinear Schr\"odinger equation with a dissipative term that accounts for the multi-photon absorption processes taking place at high enough powers in common optical media. In these beams, power and orbital angular momentum are permanently transferred to matter in the inner, nonlinear rings, at the same time that they are refueled by spiral inward currents of energy and angular momentum coming from the outer linear rings, acting as an intrinsic reservoir. Unlike vortex solitons and dissipative vortex solitons, the existence of these vortex beams does not critically depend on the precise form of the dispersive nonlinearities, as Kerr self-focusing or self-defocusing, and do not require a balancing gain. They have been shown to play a prominent role in "tubular" filamentation experiments with powerful, vortex-carrying Bessel beams, where they act as attractors in the beam propagation dynamics. Nonlinear Bessel vortex beams provide indeed a new solution to the problem of the stable propagation of ring-shaped vortex light beams in homogeneous self-focusing Kerr media. A stability analysis demonstrates that there exist nonlinear Bessel vortex beams with single or multiple vorticity that are stable against azimuthal breakup and collapse, and that the mechanism that renders these vortexes stable is dissipation. The stability properties of nonlinear Bessel vortex beams explain the experimental observations in the tubular filamentation experiments.Comment: Chapter of boo