Hybrid Activated Sludge: exploiting biochemistry to double capacity
Biddle, J., Bluewater Bio, UK
(free)
Abstract
This paper is a case study for an innovative solution that was implemented at Tsakane Wastewater Treatment Works. The objective of the project was to increase the capacity of Tsakane WWTW from 10.8 Ml/d to 20 Ml/d.
Tsakane WWTW required a capacity upgrade to meet the demands of a growing population. Over the years, the residential dwellings have increased to a point that there is no room for expansion for the plant. The existing plant has a single biological nutrient removal (BNR) reactor, and East Rand Water Company (ERWAT) developed a cost effective plan that enabled the capacity of the existing plant to double, without the need for a new module, and therefore no increase in footprint.
The project involved converting the existing BNR process to Hybrid Activated Sludge (“HYBACS”). HYBACS is a variant of conventional activated sludge that incorporates a high-rate attached-growth reactor (known as a “SMART unit”) at the front. The SMART unit can be installed offline, which offers significant benefits for construction and commissioning. The HYBACS upgrade enables the existing plant to treat 20 Ml/d to the effluent standards required, without the need for any new BNR module. This resulted in better water quality discharged as per Water Use Licence granted to the plant.
During construction, 12 SMART units, together with the steel channels, were fully assembled offsite in a local workshop. The controlled environment of the workshop meant a higher productivity, better control of raw materials and less wastage and a higher quality of overall manufacture.
The new works is not complicated and most of the equipment deployed in the HYBACS are similar to the original ones that the plant had. This makes operation and maintenance easy for ERWAT employees.
The cost of the expansion was just ZAR 6 million (approximately £330,000) per megalitre (Ml) of additional capacity provided. This represents a 40% reduction in capital budget with reference to a typical South African benchmark cost of ZAR 10 million (£560,000) per Ml for conventional upgrade methods. Furthermore, the works have a potential of 15% – 20% reduction on overall energy consumption, which have a positive variance on the operational budget.
ERWAT have concluded: “Based on the historic designs, shortage of land, increase in population in the City of Ekurhuleni, the innovative designs and technologies are efficient. They are cheaper and require shorter turnaround time to install.”
