Bioreactors for treatment of VOCs and odours – A review

Volatile organic compounds (VOCs) and odorous compounds discharged into the environment create ecological and health hazards. In the recent past, biological waste air treatment processes using bioreactors have gained popularity in control of VOCs and odour, since they offer a cost effective and environment friendly alternative to conventional air pollution control technologies. This review provides an overview of the various bioreactors that are used in VOC and odour abatement, along with details on their configuration and design, mechanism of operation, insights into the microbial biodegradation process and future R&D needs in this area.     

Application of low-cost adsorbents for dye removal – A review

Dyes are an important class of pollutants, and can even be identified by the human eye. Disposal of dyes in precious water resources must be avoided, however, and for that various treatment technologies are in use. Among various methods adsorption occupies a prominent place in dye removal. The growing demand for efficient and low-cost treatment methods and the importance of adsorption has given rise to low-cost alternative adsorbents (LCAs). This review highlights and provides an overview of these LCAs comprising natural, industrial as well as synthetic materials/wastes and their application for dyes removal. In addition, various other methods used for dye removal from water and wastewater are also complied in brief. From a comprehensive literature review, it was found that some LCAs, in addition to having wide availability, have fast kinetics and appreciable adsorption capacities too. Advantages and disadvantages of adsorbents, favourable conditions for particular adsorbate–adsorbent systems, and adsorption capacities of various low-cost adsorbents and commercial activated carbons as available in the literature are presented. Conclusions have been drawn from the literature reviewed, and suggestions for future research are proposed.     

Optimization of Fenton oxidation pre-treatment for B. thuringiensis – Based production of value added products from wastewater sludge

Fenton oxidation pretreatment was investigated for enhancement of biodegradability of wastewater sludge (WWS) which was subsequently used as substrate for the production of value- added products. The Response surface method with fractional factorial and central composite designs was applied to determine the effects of Fenton parameters on solubilization and biodegradability of sludge and the optimization of the Fenton process. Maximum solubilization and biodegradability were obtained as 70% and 74%, respectively at the optimal conditions: 0.01 ml H₂O₂/g SS, 150 [H₂O₂]₀/[Fe²⁺]₀, 25 g/L TS, at 25 °C and 60 min duration. Further, these optimal conditions were tested for the production of a value added product, Bacillus thuringiensis (Bt) which is being used as a biopesticide in the agriculture and forestry sector. It was observed that Bt growth using Fenton oxidized sludge as a substrate was improved with a maximum total cell count of 1.63 × 10⁹ CFU ml^?1 and 96% sporulation after 48 h of fermentation. The results were also tested against ultrasonication treatment and the total cell count was found to be 4.08 × 10⁸ CFU ml^?1 with a sporulation of 90%. Hence, classic Fenton oxidation was demonstrated to be a rather more promising chemical pre-treatment for Bt - based biopesticide production using WWS when compared to ultrasonication as a physical pre-treatment.     

Multi-objective optimization of waste and resource management in industrial networks – Part II: Model application to the treatment of sewage sludge

In the present article, the thermal treatment of digested sewage sludge generated in the Swiss region of Zürich is modeled and optimized from an environmental perspective. The optimization problem is solved using a multi-objective mixed-integer linear program that combines material flow analysis, process models, life cycle assessment (LCA), and mathematical optimization techniques. The treatment options include co-incineration in municipal solid waste incineration, co-processing in cement production, and mono-incineration with the prospect of phosphorus recovery. The model is optimized according to six environmental objectives. Five of the six single-objective optimal solutions involve splits over the treatment options. The results reflect the available treatment capacities and other constraints, aspects rarely considered in conventional LCA studies. Co-processing in cement production is used to the maximum extent possible when minimizing impacts on climate change, human toxicity, fossil resource depletion, and fully aggregated impacts (ReCiPe H/A), whereas mono-incineration with phosphorus recovery receives the bulk of the sludge when optimizing for ecotoxicity and mineral resource depletion. Four of the single-objective optimal solutions (minimization of fossil energy resource depletion and contribution to climate change, human toxicity, and fully aggregated impacts) outperform the reference case over the six impact categories considered, showing that the current situation can be improved in some environmental categories without compromising others. The results of the sensitivity analysis indicate that assumptions regarding the product systems displaced by recovered by-products are critical for the outcome of the optimization. Our approach identifies in all of the cases solutions in which significant environmental improvements can be attained.     

In Search of Stability – Investigating Flexible and Stable Production Strategies for an Optimised Steel Plant

It is crucial for a steel making production system to operate at the lowest possible production cost, while satisfying stability and reliability conditions. To plan future production strategies, it is therefore important to be able to model the system behaviour when internal and external parameters are changed. In this study the sensitivity and stability of an optimised solution, of an integrated steel plant, have been investigated. The solution’s sensitivity has been analysed taking both internal process changes and external price variations into account, through applying both simulation and optimisation. The analysis also includes both costs and environmental issues such as carbon dioxide and sulphur emissions. Based on the methodology suggested, it is possible to determine the stability of the system solution, including both economic and environmental performance.     

A review on the production of fermentable sugars from lignocellulosic biomass through conventional and enzymatic route—a comparison

The scarcity of fossil fuels has urged the economically developed countries to find the resources for an alternative energy sources. In apprehension to this, biofuels, like bioethanol and biobutanol, produced from lignocellulosic biomass were considered as potential alternative. There are several methods for the pretreatment of biomass before it is being used as a feedstock for the production of fermentable sugars. However, one of the crucial concerns here is to enumerate an economic pretreatment scheme that can be implemented in large scale for the production of mostly exposed cellulosic part from biomass. This will ensure an effective hydrolysis of cellulose for the production of fermentable sugars and the production of biobutanol from these derived sugars. Moreover, the keynote understanding of an effective fermentation is the production of less inhibitory compounds like furfural, hydroxymethyl furfural during the hydrolysis of cellulose. Enzymatic hydrolysis of cellulose was reported as the most efficient method is this aspect. Trichoderma sp. was found the mostly used resources for the enzyme called cellulase and Aspergillus sp. for hemicellulase enzymes. The most crucial part here is the isolation of proper enzyme that will increase the rate of hydrolysis. Moreover, selection of proper pretreatment process will be a key benefit to the production of fermentable sugars through enzymatic hydrolysis. Based on the biomass nature, the evaluated hot water pretreatment followed by enzymatic hydrolysis with a provision of enzyme reusability (like encapsulated or enzyme separation with membrane) seems to be promising for enhanced biofuel-production.     

A model for assessing habitat fragmentation caused by new infrastructures in extensive territories – Evaluation of the impact of the Spanish strategic infrastructure and transport plan

The aim of the present work is to design a model for evaluating the impact of planned infrastructures on species survival at the territorial scale by calculating a connectivity index. The method developed involves determining the effective distance of displacement between patches of the same habitat, simplifying earlier models so that there is no dependence on specific variables for each species. A case study is presented in which the model was used to assess the impact of the forthcoming roads and railways included in the Spanish Strategic Infrastructure and Transport Plan (PEIT, in its Spanish initials).This study took into account the habitats of peninsular Spain, which occupies an area of some 500,000 km². In this territory, the areas deemed to provide natural habitats are defined by Directive 92/43/EEC. The impact of new infrastructures on connectivity was assessed by comparing two scenarios, with and without the plan, for the major new road and railway networks. The calculation of the connectivity index (CI) requires the use of a raster methodology based on the Arc/Info geographical information system (GIS). The actual calculation was performed using a program written in Arc/Info Macro Language (AML); this program is available in FragtULs (Mancebo Quintana, 2007), a set of tools for calculating indicators of fragmentation caused by transport infrastructure (http://topografia.montes.upm.es/fragtuls.html).The indicator of connectivity proposed allows the estimation of the connectivity between all the patches of a territory, with no artificial (non-ecologically based) boundaries imposed. The model proposed appears to be a useful tool for the analysis of fragmentation caused by plans for large territories.     

A comparison of two models for dealing with urban solid waste: Management by contract and management by public–private partnership

In work, we compared two models for dealing with urban solid waste in Brazil, namely, management by contract and management by public–private partnership. Management by contract, which is widely used by the public sector (municipalities) for urban solid waste collection and disposal and for acquiring goods and services for periods not greater than 60 months, is governed by Federal Law 8.666/93. Management by public–private partnership is governed by Federal Law 11.079/04 for contracts worth more than US$11,000,000 and involves costs for the private partner and public partner. The financial return for the private partner must be clearly delineated and the contract should last from 5 to 35 years. Management by public–private partnership that involves the management of municipal solid waste is very recent in Brazil. For this reason, the comparison between the two forms of management of municipal solid waste (management by contract and management by public–private partnership) described in this work is unprecedented in this country. Both of these models are used in the municipality of São Bernardo do Campo in the State of São Paulo, Brazil. For this study, information was gathered through semi-structured interviews with public works managers in São Bernardo do Campo, with members of an Association of Recyclable Material Collectors and with managers of a company contracted by the São Bernardo do Campo city hall, and also by researching public documents provided by the city hall. The interviews with the managers of the municipality of São Bernardo do Campo, the Association and the company were held in the headquarters of each institution. The documents analyzed, such as the plan for dealing with municipal solid waste, contracts and bids were made available electronically. Analysis of the results indicated that management by a public–private partnership was more advantageous for dealing with urban solid waste than management by contract since the former provided a strong selective collection program, reduced the amount of solid waste sent to sanitary embankments, led to the recovery an area of land previously degraded by the incorrect disposal of urban solid waste and stimulated the installation of an energy recovery unit.