Renovation of food-processing wastewater by a Riparian wetland

Abstract

Treated wastewater from a food-processing plant, together with intermittent outflow from a hyPereutrophic pond, were discharged over a 20-year Period to a cattail-dominated wetland and hence to a small stream. Organics and nutriet levels in the effluent were comparable to levels in domestic wastewater. Fifteen variables were monitored upstream and downstream from the plant over 18 months. Means for most variables were slightly higher downstream, but differences between stations were not statistically significant. Wetland processing of nitrogen was markedly affected by a change from drought to flood conditions. After accounting for dilution, the overall effect of the wetland on the effluent was to reduce biological oxygen demand 43.7%, ammonia N 46.3%, nitrate/nitrite N 17.4%, and conductivity 15.6%. However, total suspended solids were increased 41.4%, total organic nitrogen 28.8%, and total phosphorus 24.7%. It was concluded that the wetland effectively renovated the effluent but that removal efficiency would be improved if the effluent were pretreated to reduce phosphorus and dispersed to increase residence time in the wetland.

The Ecology of Interfaces: Riparian Zones

“…An increasingly important managerial use of riparian zones is to control diffuse pollution. Riparian zones are more effective over the long term when upstream pollution has been limited through good agricultural practices at the catchment level (7,51). The integrated effects of riparian zones on water quality will also differ according to stream order, smaller streams having a greater potential than larger ones to buffer against diffuse pollution (145).…”

“…For example, zone 1 of the multispecies riparian buffer strip (located near the stream) functions better if zone 2 is harvested infrequently; and zone 3, near the cropland, also functions better if accumulated sediment is removed and herbaceous vegetation is reestablished periodically (145). The literature, however, offers divergent examples ranging from efficient removal of nitrogen after 20 years of high nutrient loading (7) to exhaustible sinks (41). Whatever the example, improved land use practices within the catchment and the maintenance of riparian zones for interception of groundwater flows by vegetation in various stages of succession (which differ in absorption capacity) are key factors for the long-term vitality of buffer strips and streams (98,270).…”

Hydrology and cycling of nitrogen and phosphorus in Little Bean Marsh: A remnant riparian wetland along the Missouri River in Platte County, Missouri, 1996–97

“…Wetland nutrient studies have a wide range of nutrient removal rates and processing characteristics depending on wetland characteristics-especially hydrology (Gosselink and Turner, 1978;Mitsch and Gosselink, 1993). Numerous studies have shown that some wetlands actually are net nutrient sources or nutrient transformers (Peverly, 1982;Elder, 1985;Baillie, 1995). Only three water-quality studies have been undertaken in wetlands along large rivers in Missouri, and none of these studies collected hydrologic data needed to explain many nutrient cycling phenomena.…”