Handling of wet residues in industry

In countries with high prices of fresh water use and wastewater discharge, water recycling has become an alternative to traditional water consumption and discharge for industries with water-based processes. Industrial water recycling means in many cases that water has to be treated and cleaned, to remove from it the substances which presence impedes reusing the water. These substances accumulate in a by-product called wet residue. An integral part of water recycling projects in the industry is the handling and disposal of the wet residues generated. The treatment, utilisation and disposal of wet residues depend totally on the industrial sector of origin and the composition of the water to be recycled. Treatment is more problematic in some cases than in others, but in all water recycling applications it is an issue of concern. The present study addresses this concern by providing a package of operational tools geared to assist industries in the selection of disposal routes for wet residues. The target group of the study are the wet residue producing companies. The study is structured in the form of a handbook, with the aim of making it simpler and faster for industries to find their way to characterise the technical options, the costs, and the legal, environmental and social implications of residue disposal. The handbook contains a series of decision-support tools that enables a company to select a solution. In this way, wet residue handling can be tackled at an early phase of project design, avoiding that it becomes a hurdle at a later stage in project implementation. The easiness or difficulty of finding a feasible disposal route is connected to the residue’s composition, the characteristics of the production site, and local constraints of different nature such as climate, geology, distance to water bodies and uses of such bodies, distance to available agricultural land, characteristics of the local wastewater treatment plant, local and national legislation, or availability of subsidies. This study uses as example the geographical, legislative, economic and social boundary conditions currently existing in Denmark. Not all disposal routes can be used for treating all residue types in all locations due to e.g. legislative, geographical or social considerations. In most applications and most locations, only some of the disposal routes will be available, and from those only a few will be feasible considering also economic and environmental criteria. It has been found that the advantages and disadvantages of a given disposal option, as a basis for decision-making, can be analysed using five assessment criteria:  legislation  technology  economy  environment  society concerns These five assessment criteria have been used as a basis for developing a model which objective is to support a company in assessing the feasibility of a given disposal route for the treatment of their wet residue, and in deciding between different disposal routes. The decision model comprises the use of five assessment tools, each of them addressing one of the five mentioned criteria. The use of the tools in practice is illustrated with three case studies carried out for Danish companies involved in projects of water recycling. In addition to the five assessment criteria, a good characterisation of the residue is fundamental in most disposal routes for clarifying the possibility of treating the residue. The better the characterisation from the start is, the easier the assessment of the feasible disposal alternatives becomes. The decision about the handling/disposal solution for the residue is a trade-off between the quality of the residue and the treatment costs necessary to achieve that quality. The quality of the wet residue is defined in the form of acceptance criteria by the potential residue hosts (waste treatment facilities, industrial processes), or discharge criteria defined by the authorities. The treatment costs depend on the geographical availability of the array of potential disposal options, and the technology needed to implement to fulfil the acceptance criteria. The general rule that guides the choice of a disposal route in the company is the consideration of the residue’s constituents as a resource and not as waste. However, companies can be required by authorities to document the environmental feasibility of any utilisation or disposal route different than those ordinarily established for industrial waste. The final decision on implementation of a disposal route is the result of a combined consideration of the inputs from the technical, economic and environmental assessments, supplemented with the information of the legislative requirements for compliance, and information from relevant stakeholders. The weight that a company assigns to each of these five categories is part of the company’s internal policy, and can depend on factors such as the investment capacity, the relationships with the stakeholders, or the promotion of its environmental profile.