Anaerobic pond sludge profiling and trigger point determination

Abstract

The accumulation of sludge in anaerobic effluent treatment ponds used at the majority of Australian piggeries has proved to be a difficult issue to manage effectively for several decades. While the sludge has a significant value as an organic fertiliser and soil amendment, in many instances, producers have delayed removing sludge from their anaerobic ponds, resulting in the accumulation of large volumes of highly dense sludge deposits which have proven to be extremely difficult and expensive to remove; particularly from large, deep ponds. As the sludge progressively accumulates over time, the treatment capacity of an anaerobic pond decreases. This potentially results in; increased odour emission, ineffective treatment of piggery effluent, and carryover of solids into secondary effluent storage ponds. Furthermore, the solids content and viscosity of the sludge increase with storage time and depth within the sludge profile. Consequently, desludging ponds, which have not had any sludge removed for periods over five years, can prove to be very difficult, time consuming and expensive.

Several factors have constrained producers from effectively managing sludge. These include; the lack of reliable Australian data on sludge accumulation rates, pond designs which have not adequately considered the need for periodic desludging, lack of relatively simple and inexpensive technology for effectively monitoring sludge levels in anaerobic ponds, lack of reliable information and knowledge regarding effective desludging methods, lack of guidance on the most appropriate timing of desludging for ease of removal, without significantly reducing the energy potential of sludge stored in covered anaerobic ponds (CAPs), lack of experienced desludging contractors with suitable machinery in some regional/rural areas, and the significant costs involved in employing desludging contractors and/or labour costs to carry out desludging operations. The major objectives of this project were to address the constraining factors outlined above.