Technical and Economic Analysis of Stabilization Ponds

Abstract

Compared with other methods of wastewater treatment, stabilization ponds provide the advantages of low capital cost, low operation and maintenance (O&M) costs and simple manipulations at the expense of a large land area. This study analysed the technical and economic aspects of stabilization ponds in order to determine their recommendation for use in specific location. Since few stabilization ponds in China were self-designed, and few integrated cost data were available, cost data were determined by a set of series designs. Stabilization ponds are contrasted with activated sludge (AS) system, since AS is a more frequently used method for municipal wastewater treatment. The cost data for AS system were obtained by surveying AS facilities built in China. The aspects used in this model analysis included (1) capital cost, (2) O&M costs, and (3) occupied land cost. For comparing the total costs of stabilization pond and AS, a new concept, critical land price (Pro), was introduced. Pro is the price of land at which the total cost of a stabilization pond is equal to that of an equivalent AS system. When land price is above the Pro, AS is more economic than a stabilization pond. When land price is below the Pro, a stabilization pond is more economic. In addition to comparing the total costs of AS and stabilization ponds, a comparison was made between stabilization pond in South China and in North China. The capital cost of a stabilization pond is 1/3 to 1/2 that of an equivalent AS plant, the O&M costs are 1/5 to 1/4 the AS costs, and the occupied land area is 15 to 40 times the AS land area. The Pro decreases with increasing wastewater flow. Using the model analysis, the critical land price in South China (Pros) is in the range of 10,000 to 30,000 RMB/Mo. (Mo. is an area unit used in China, it is equal to 1/15 hectares.) In North China, the critical land price (Pron) is 6,000 to 16,000 RMB/Mo. Comparing stabilization ponds in the south with those in the north showed that the capital cost, 0&M costs, and occupied land cost in the north are 1.5 to 1.8 times, 1.5 times, and 1.6 to 1.7 times those in the south, respectively.