Biosolids drying at Christchurch wastewater treatmant plant - A sustainable solution

Christchurch City Council has traditionally disposed of wastewater treatment plant biosolids by spreading on forestry land and more recently in rehabilitating a closed landfill. With both of these options operating on a limited timeframe Christchurch has had to develop a new strategy for biosolids management with a 20 year time horizon. The new strategy has been developed with a focus on meeting key Council objectives which include:

• Optimising biosolids reuse potential
• Minimizing carbon footprint
• Managing Council costs and risks
• Meeting social and cultural objectives

This paper explores sustainability themes in biosolids management and outlines the process involved in selecting and evaluating a preferred biosolids management option for Christchurch for the next 20 years. The main features of the option the council chose to implement, thermal belt drying, as well as some aspects of project implementation are described, including:

• A dual-line belt drying plant, designed and built by Klein of Germany
• An energy centre providing heat for the dryer, designed and operated by Energy for Industry
• Utilisation of 100% renewable fuels including landfill gas, biogas and wood
• Reuse of dried biosolids in mine rehabilitation - Delivery through Design-Build and Design-Build-Operate Contracts