Carlo Collivignarelli

The influence of different disinfectants on mutagenicity and toxicity of urban wastewater

Many human pathogenic micro-organisms can be transmitted by waters contaminated by wastewater effluents. Wastewater disinfection helps prevent the spread of these pathogens in aquatic environments. Chlorination is the most widely used method for the disinfection of wastewater, but can cause the formation of mutagenic/carcinogenic and toxic by-products which are potentially harmful to human and aquatic organisms. The aim of this research was to study the influence of disinfectants alternative to chlorine, such as chlorine dioxide, ozone, peracetic acid and UV radiation, on the formation of mutagenic and toxic compounds in wastewater. Wastewater samples were collected before and after disinfection in summer and in winter and then adsorbed using silica C18 cartridges. Concentrates were tested for mutagenicity using the Ames test. For toxicity test, a bioluminescence assay using Vibrio fischeri photobacteria was employed. To detect DNA damage activity non-concentrated water samples were tested using two genotoxicity plant tests (Allium test and Tradescantia/micronuclei test). All disinfectant treatments produced bacterial mutagenicity, particularly after treatment with ClO2 or ozone. The Allium cepa test gave positive results only for PAA-treated wastewater sampled in winter and the Tradescantia/MCN test always gave negative results. Raw wastewater, ClO2- and PAA-disinfected waters showed toxic effects in the marine bacteria test.

Recovery of MSWI and soil washing residues as concrete aggregates.

The aim of the present work was to study if municipal solid waste incinerator (MSWI) residues and aggregates derived from contaminated soil washing could be used as alternative aggregates for concrete production. Initially, chemical, physical and geometric characteristics (according to UNI EN 12620) of municipal solid waste incineration bottom ashes and some contaminated soils were evaluated; moreover, the pollutants release was evaluated by means of leaching tests. The results showed that the reuse of pre-treated MSWI bottom ash and washed soil is possible, either from technical or environmental point of view, while it is not possible for the raw wastes. Then, the natural aggregate was partially and totally replaced with these recycled aggregates for the production of concrete mixtures that were characterized by conventional mechanical and leaching tests. Good results were obtained using the same dosage of a high resistance cement (42.5R calcareous Portland cement instead of 32.5R); the concrete mixture containing 400 kg/m(3) of washed bottom ash and high resistance cement was classified as structural concrete (C25/30 class). Regarding the pollutants leaching, all concrete mixtures respected the limit values according to the Italian regulation.

A Comparison Among Different Wastewater Disinfection Systems: Experimental Results

In this work, the efficiency and the applicability of some disinfection systems for biologically treated wastewater were studied. The following disinfection processes were considered: peracetic acid (PAA), chlorine dioxide, ozone, UV light. These treatments were chosen as an alternative to chlorination. Their applicability was investigated considering both the removal efficiency of microorganisms and the qualitative changes in the treated effluent (e.g. presence of disinfectant residues, disinfection by-products, etc.). The different processes were tested by means of pilot scale plants working in parallel; in fact they were fed with the same wastewater (secondary effluent of a municipal wastewater treatment plant). Finally, an economical analysis was carried out.

Agricultural waste as household fuel: Techno-economic assessment of a new rice-husk cookstove for developing countries

In many rural contexts of the developing world, agricultural residues and the organic fraction of waste are often burned in open-air to clear the lands or just to dispose them. This is a common practice which generates uncontrolled emissions, while wasting a potential energy resource. This is the case of rice husk in the Logone Valley (Chad/Cameroon). In such a context household energy supply is a further critical issue. Modern liquid fuel use is limited and traditional solid fuels (mainly wood) are used for daily cooking in rudimentary devices like 3-stone fires, resulting in low efficiency fuel use, huge health impacts, increasing exploitation stress for the local natural resources. Rice husk may be an alternative fuel to wood for household energy supply. In order to recover such a biomass, the authors are testing a proper stove with an original design. Its lay-out (featuring a metal-net basket to contain the fuel and a chimney to force a natural air draft) allows a mix of combustion/gasification of the biomass occurring in a completely burning fire, appropriate for cooking tasks. According to results obtained with rigorous test protocols (Water Boiling Test), different lay-outs have been designed to improve the performance of the stove. Technical and economic issues have been addressed in the development of such a model; building materials have been chosen in order to guarantee a cost as low as possible, using locally available items. The feasibility of the introduction of the stove in the studied context was assessed through an economic model that keeps into account not only the technology and fuel costs, but also the energy performance. According to the model, the threshold for the trade-off of the stove is the use of rice husk to cover 10-15% of the household energy needs both with traditional fireplaces or with improved efficiency cookstoves. The use of the technology proposed in combination with improved woodstove would provide householders with an appropriate and convenient cooking technology portfolio, increasing the opportunities of choice of the preferred energy system for the user and allowing significant savings for the family budget (up to 50% of the total annual cooking energy expenditure). The proposed model may be used also as a tool for the evaluation of the affordability or for the comparison of different cooking technologies also in other similar contexts, given their specific techno-economic parameter values.

Ammonia stripping from MSW landfill leachate in bubble reactors: process modeling and optimization

This work presents a study of the ammonia air stripping pro cess in a semi-flow batch bubble reactor as a pre-treatment for municipal solid waste (MSW) landfill leachate. In order to assess the optimum treatment conditions from a technical and an economic point of view, the research was carried out in the following steps: 1) experimentation in a pilot plant; 2) mathematical model development; and 3) economic analysis. The experimentation showed that it is possible to achieve high ammonia removal efficiencies even without basificant dosage, if temperature is maintained between approximately 60 and 70°C. The development and calibration of a mathe matical model permitted the study to determine the treat ment efficiency of the process under several operating condi tions. The economic analysis has shown that, with a removal efficiency of approximately 70%, it is convenient to work without basificant dosage and at a temperature of 70°C. These conditions can also be considered optimal from a tech mcal point of view.

From mixed to separate collection of solid waste: Benefits for the town of Zavidovići (Bosnia and Herzegovina)

In Bosnia and Herzegovina only 50% of the municipalities have a well-organized service for (mixed) waste collection and disposal. Illegal dumping is very common, in particular in rural areas, which are not regularly served by any service of collection. This situation leads to serious risks for public health and has dangerous environmental impacts. In Zavidovići the municipality is trying to meet high standards in the delivery of services of waste collection, but is constrained by scarce financial and technical resources. Different scenarios for the implementation of a system of separate collection in Zavidovići were elaborated in order to provide a useful tool for decision making by comparing costs and environmental & economic benefits of each scenario. Six scenarios were considered, based on different recovery rates for plastic, paper & cardboard, and metals. Benefits resulting from the implementation of each of the proposed scenarios are compared in terms of savings of landfill volume and costs. The study concludes that the adoption of a system of separate collection could generate positive impacts on all the stakeholders involved in the solid waste management sector in Zavidovići and could contribute to the compliance of European standards in many Central and Eastern European countries as established by a number of national environmental protection strategies.

Influence of drinking water treatments on chlorine dioxide consumption and chlorite/chlorate formation

Disinfection is the last treatment stage of a Drinking Water Treatment Plant (DWTP) and is carried out to maintain a residual concentration of disinfectant in the water distribution system. Chlorine dioxide (ClO2) is a widely used chemical employed for this purpose. The aim of this work was to evaluate the influence of several treatments on chlorine dioxide consumption and on chlorite and chlorate formation in the final oxidation/disinfection stage. A number of tests was performed at laboratory scale employing water samples collected from the DWTP of Cremona (Italy). The following processes were studied: oxidation with potassium permanganate, chlorine dioxide and sodium hypochlorite, coagulation/flocculation with ferric chloride and aluminum sulfate, filtration and adsorption onto activated carbon. The results showed that the chlorine dioxide demand is high if sodium hypochlorite or potassium permanganate are employed in pre-oxidation. On the other hand, chlorine dioxide leads to the highest production of chlorite and chlorate. The coagulation/flocculation process after pre-oxidation shows that chlorine dioxide demand decreases if potassium permanganate is employed as an oxidant, both with ferric chloride and aluminum sulfate. Therefore, the combination of these processes leads to a lower production of chlorite and chlorate. Aluminum sulfate is preferable in terms of the chlorine dioxide demand reduction and minimization of the chlorite and chlorate formation. Activated carbon is the most effective solution as it reduced the chlorine dioxide consumption by about 50% and the DBP formation by about 20-40%.

Techno-economic evaluation for the improvement of MSW collection in Somaliland and Puntland

This paper is based on a study, which aim is to provide an overview of the current MSW management in the main cities in Somaliland and Puntland and to identify strategies to improve the present situation. In particular, this article illustrates assessments concerning waste collection and technical solutions identified for its improvement, whereas waste treatment and disposal phases will be discussed in a further paper. The survey, which has been carried out in close collaboration with local administrators and technicians, has shown that MSW management is very lacking and needs both structural and operational actions. Waste collection in the surveyed cities covers 65% of population at its best, whereas it is substantially absent in Gardo and Sheik. The extension of waste collection service to the entire population of each city would need investment costs varying between 17,500 USD for Sheik and 200,000 USD for Galkayo, whereas total operational costs would vary between 1.17 USD/ inh/y in Boroma and 5.73 USD/inh/y in Garowe. Anyway, technical interventions are necessary to provide a larger number of citizens with a regular waste collection service and they should be preceded and accompanied by public awareness campaigns on environmental protection and capacity building services addressed to local administrators and technicians.

Method for technical, economic and environmental assessment of advanced sludge processing routes

The legislative framework in force in Europe entails restrictive effluent standards for sensitive areas, and quite severe restrictions on the properties of residual sewage sludge, both for landfill disposal and for agricultural use. Several technologies and management strategies have been proposed and applied in wastewater treatment plants to minimise sludge production and contamination. However, their techno-economic and environmental performance has to be carefully evaluated. The ROUTES project, funded within the EU Seventh Framework programme, aims to find new routes for wastewater treatment and sludge management and thereby guide EU members in their future choices. Within this project, the authors have developed and applied a procedure for techno-economic-environmental assessment of new wastewater and sludge processing lines in comparison to reference plants. The reference plants are model conventional plants that experience different types of problems and the new plants are modified plants in which different innovative technologies have been added to solve these problems. The procedure involves a rating of selected technical issues, estimates of operating costs and an assessment of environmental impacts from a life cycle perspective. This paper reports on the procedure and shows examples of results.

Process Improvement and Energy Saving in a Full Scale Wastewater Treatment Plant: Air Supply Regulation by a Fuzzy Logic System

Achieving good performance in air supply control is an important goal in the management of wastewater treatment plants, whose highly nonlinear behaviour makes the application of conventional control techniques problematic. This paper presents the development and experimentation of a fuzzy logic system for air supply regulation in a full scale municipal wastewater treatment plant. The system is composed of two main modules, one devoted to continuously adjusting the DO set point on the basis of the current effluent NH4 +-N concentration (on-line measurement), and the other devoted to achieve the DO set point by controlling air supply devices. The experiment was carried out on the plant for about one year, leading to significant advantages in terms of both process stability and energy saving.