Water Pollution: the Treatment and Management

A technology was developed to provide better treatment as science advanced our knowledge of aquatic life mechanisms and human health effects. The need for purer water was also identified. Heavy metals, toxic chemicals, and other pollutants can now be removed from domestic and industrial wastewater to an increasingly greater degree. Methods of advanced treatment include microfiltration, carbon adsorption, evaporation/distillation, and chemical precipitation.

Sludge Management

In sludge management, the greatest uncertainty about future trends lies in the prospects for recycling sewage sludge in agriculture.

This is due to political and environmental concerns about this practice, as well as tightening legislation. Strategically, this is the most important outlet for sludge and is the most environmentally sustainable from a resource recycling perspective. However, the future of agricultural reuse depends on adopting pragmatic controls that facilitate land application while protecting the environment, based on sound scientific principles and risk assessment. Counteracting prejudicial perceptions about sludge and gaining consumer confidence that land application is a safe and acceptable practice —one that represents the best approach to sludge management— is crucial. As the availability of outlets for sludge diminishes, providing secure, cost-effective, and environmentally acceptable approaches to sludge management becomes ever more challenging. This highlights the importance of maintaining the land application route to allow the beneficial reuse of sludge. Otherwise, the only remaining viable alternative will be the construction of more sludge incinerators in urban areas, with ash disposal to landfill.

The treatment and management of sewage sludge present technical and perception challenges, with costs associated representing more than 50% of total wastewater treatment expenses (Kroiss, 2004). Thus, sludge production is often viewed as a disadvantage and should be minimized as far as possible. However, sludge produced from wastewater treatment presents a range of resource recovery opportunities. Some of these, such as the reuse of sludge biosolids as fertilizer products in agriculture, are well established. Others—like the generation of biogas and renewable energy from sludge anaerobic digestion (AD)—have yet to be fully maximized. There are even more resource recovery options which have yet to be realized, and together, they can offset the resource demands of the AS process. Recycling sludge through land application, for agricultural use or other purposes such as restoration, and sludge disposal in a landfill, are the two primary final destination routes for sewage sludge management in Europe.

Separate statistics are collected on the incineration of sludge, but this is not a disposal route per se. Incineration is effectively a sludge treatment process that achieves maximum solids reduction by thermal conversion, with the residual ash disposed of in a landfill. Energy production from sludge incineration processes is used for water evaporation and to meet the parasitic load of the process. Therefore, incineration does not usually contribute to improved energy management (Mininni et al., 1997; Thierbach and Hanssen, 2002; Kroiss, 2004). Generally, the disposal of whole sludge in a landfill is limited and viewed as unsustainable in the long term, as well as inconsistent with EU landfill policy to reduce the disposal of biodegradable municipal waste by this route. Nevertheless, it represents a significant disposal route in some cases. There is also uncertainty about the final destinations for sludge in some European countries, as suggested by the large ‘others’ category in some reports.

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