Wind-aerated lagoons for sustainable treatment of wastewaters from small communities

Biological treatment processes that milise wind-aerated lagoons have proved popular for small communities because of their negligible sludge production. Scottish Water has recently constructed one such system, known as the Aero-Fac (North Dakota, USA), and this paper reports on an intensive 12-month study designed to both monitor the lagoon performance and establish the key design parameters. Over the monitoring period the final effluent complied with both Scottish Environmental Protection Agency discharge consents and Scottish Water performance guarantees for biochemical oxygen demand and total suspended solids, which averaged 9 and 28mg/L, respectively. The lagoons showed an accelerated growth of algae during the summer months, but this did not adversely affect the final effluent suspended solids. The lagoons also achieved a faecal coliform removal of around 3.4 log and an average effluent ammonia of 7.6 mg/L. However, the ammonia removal was seasonal with a better performance in the summer months, which probably reflects take-up by the growing algal population over this period. No sludge was wasted from the lagoon over the monitoring period yet it accumulated only sparingly in the lagoons, mainly around the inlet of the primary lagoon. The estimated per capita sludge accumulation rate was 0.0047 m(3)/person/year. The total capital costs of,the scheme were 1.65 pound million, and of this the lagoon cost was 840 pound 000. The capital costs of 420 pound per capita make this more expensive than other, similar options, but plant operating costs are significantly reduced.