Performance and Upgrading Alternatives for Water Pollution Control Plants Discharging to Severn Sound

Discharges from municipal water pollution control plants have been identified as major point source inputs of phosphorus to Severn Sound. For the 2-year period 1989–90, the estimated total phosphorus loading from eight water pollution control plants discharging directly or indirectly to Severn Sound exceeded 6,200 kg/year. A review of options available and the relative costs of reducing total phosphorus loadings from these facilities was conducted. It was found that a 59% reduction could be achieved by process modifications at relatively small capital costs. Further improvements would require major capital investment. Large differences in the cost per kg of phosphorus removed were identified between plants. The cost data suggest that it would be more cost effective to impose more stringent effluent limits at some plants than at others. The most cost-effective strategy depends on the total phosphorus load limit which must be achieved to maintain the desired receiving water quality; however, this strategy may not involve the application of the same effluent limits at all facilities discharging to Severn Sound.