Low-cost filter media for removal of hydrogensulphide from piggery biogas

The presence of elevated concentrations of hydrogen sulphide (H2S) in piggery biogas is problematic due to its corrosiveness and toxicity. At small scale, the cost of using iron or carbon-based commercial filter media to remove H2S can act as a barrier to the uptake of on-farm biogas technology. To identify cost-effective, alternative options, this study tested and compared H2S removal by the commercial iron-oxide H2S scavenger (cg5) with the alternative solid media: granulated steel furnace slag (GSFS), red soil, compost, composted beef feedlot manure, granular activated carbon (GAC) and biochar. Experiments measured single-pass H2S removal from a pre-humidified standard gas (2000 ppm H2S in nitrogen) onto solid media contained in a cylindrical plastic column (DN 25 mm, depth 110–147 mm). The commercial medium (cg5) performed considerably better than the other media, achieving sulphur removal of 143 g S/kg medium at breakthrough (>10 ppm outlet H2S). A red soil was the most promising alternative medium (2–12 g S/kg medium at breakthrough). The crystalline structure of the iron-oxide minerals appeared to strongly influence the H2S removal capacity of the red soils, and pressure drop was generally high. Bulking with ground sugarcane mulch (SCM) was effective at reducing pressure drop. Interestingly, H2S removal with red soil improved when the soil was regenerated by exposure to air, followed by reuse in the column. Overall, red soil may be a suitable low-cost option, especially for polishing biogas after initial biological H2S removal

Quantifying the sensitivity of soil microbial communities to silver sulfide nanoparticles using metagenome sequencing

Soils are a sink for sulfidised-silver nanoparticles (Ag₂S-NPs), yet there are limited ecotoxicity data for their effects on microbial communities. Conventional toxicity tests typically target a single test species or function, which does not reflect the broader community response. Using a combination of quantitative PCR, 16S rRNA amplicon sequencing and species sensitivity distribution (SSD) methods, we have developed a new approach to calculate silver-based NP toxicity thresholds (HCx, hazardous concentrations) that are protective of specific members (operational taxonomic units, OTUs) of the soil microbial community. At the HC20 (80% of species protected), soil OTUs were significantly less sensitive to Ag₂S-NPs compared to AgNPs and Ag+ (5.9, 1.4 and 1.4 mg Ag kg-1, respectively). However at more conservative HC values, there were no significant differences. These trends in OTU responses matched with those seen in a specific microbial function (rate of nitrification) and amoA-bacteria gene abundance. This study provides a novel molecularbased framework for quantifying the effect of a toxicant on whole soil microbial communities while still determining sensitive genera/species. Methods and results described here provide a benchmark for microbial community ecotoxicological studies and we recommend that future revisions of Soil Quality Guidelines for AgNPs and other such toxicants consider this approach.Casey L. Doolette, Vadakattu V. S. R. Gupta, Yang Lu, Justin L. Payne, Damien J. Batstone, Jason K. Kirby, Divina A. Navarro, Mike J. McLaughli

Methanosarcinaceae and acetate-oxidizing pathways dominate in high-rate thermophilic anaerobic digestion of waste-activated sludge

This study investigated the process of high-rate, high-temperature methanogenesis to enable very-high-volume loading during anaerobic digestion of waste-activated sludge. Reducing the hydraulic retention time (HRT) from 15 to 20 days in mesophilic digestion down to 3 days was achievable at a thermophilic temperature (55°C) with stable digester performance and methanogenic activity. A volatile solids (VS) destruction efficiency of 33 to 35% was achieved on waste-activated sludge, comparable to that obtained via mesophilic processes with low organic acid levels

Phosphorus recovery: a need for an integrated approach

Increasing cost of phosphate fertilizer, a scarcity of high quality phosphate rock (PR)and increasing surface water pollution are driving aneed to accelerate the recovery and re-use ofphosphorus (P) from various waste sectors. Options to recover P occur all along the open P cycle from mining to households to oceans. However, P recovery as a regional and global strategy towards P sustainability and future food, bio energy and water security is in its infancy because of a number of technological, socio-economic and institutional constraints. There is no single solution and resolving these constraints requires concerted collaboration betweenrelevant stakeholders and an integrated approach combiningsuccessful business models withsocio-economic and institutional change. We suggest that an operational framework is developed for fast tracking cost-effective recovery options

A plant wide aqueous phase chemistry model describing pH variations and ion speciation/pairing in wastewater treatment process models

There is a growing interest within the Wastewater Treatment Plant (WWTP) modelling community to correctly describe physico–chemical processes after many years of mainly focusing on biokinetics. Indeed, future modelling needs, such as a plant-wide phosphorus (P) description, require a major, but unavoidable, additional degree of complexity when representing cationic/anionic behaviour in Activated Sludge (AS)/Anaerobic Digestion (AD) systems. In this paper, a plant-wide aqueous phase chemistry module describing pH variations plus ion speciation/pairing is presented and interfaced with industry standard models. The module accounts for extensive consideration of non-ideality, including ion activities instead of molar concentrations and complex ion pairing. The general equilibria are formulated as a set of Differential Algebraic Equations (DAEs) instead of Ordinary Differential Equations (ODEs) in order to reduce the overall stiffness of the system, thereby enhancing simulation speed. Additionally, a multi-dimensional version of the Newton–Raphson algorithm is applied to handle the existing multiple algebraic inter-dependencies. The latter is reinforced with the Simulated Annealing method to increase the robustness of the solver making the system not so dependant of the initial conditions. Simulation results show pH predictions when describing Biological Nutrient Removal (BNR) by the activated sludge models (ASM) 1, 2d and 3 comparing the performance of a nitrogen removal (WWTP1) and a combined nitrogen and phosphorus removal (WWTP2) treatment plant configuration under different anaerobic/anoxic/aerobic conditions. The same framework is implemented in the Benchmark Simulation Model No. 2 (BSM2) version of the Anaerobic Digestion Model No. 1 (ADM1) (WWTP3) as well, predicting pH values at different cationic/anionic loads. In this way, the general applicability/flexibility of the proposed approach is demonstrated, by implementing the aqueous phase chemistry module in some of the most frequently used WWTP process simulation models. Finally, it is shown how traditional wastewater modelling studies can be complemented with a rigorous description of aqueous phase and ion chemistry (pH, speciation, complexation)

The difference that tenure makes

This paper argues that housing tenures cannot be reduced to either production relations or consumption relations. Instead, they need to be understood as modes of housing distribution, and as having complex and dynamic relations with social classes. Building on a critique of both the productionist and the consumptionist literature, as well as of formalist accounts of the relations between tenure and class, the paper attempts to lay the foundations for a new theory of housing tenure. In order to do this, a new theory of class is articulated, which is then used to throw new light on the nature of class-tenure relations

Contested resources: unions, employers, and the adoption of new work practices in US and UK telecommunications

The pattern of adoption of high-performance work practices has been explained in terms of strategic contingency and in terms of union presence. We compare the post-deregulation/privatization changes in work practice at AT&T, Bell Atlantic and British Telecom. On the basis of these cases, we argue that the choice of new work practices should be understood as a consequence not only of the company's resources or changes in its environment, nor of a simple union presence, but also as a consequence of the practices' effects on union power, the nature of the union's engagement, and the union's strategic choices