Wetlands Assimilation of Treated Domestic Sewage for Ecological Restoration and Storm Surge Protection - Public Health Aspects

This paper summarizes the findings of a pre-design feasibility analysis assessing the restoration of significant portions of wetlands in southeast Louisiana by providing nutrients through the introduction of treated municipal wastewater effluent. Wetlands assimilation is a process whereby properly treated and disinfected municipal wastewater treatment plant effluent is used to provide a source of freshwater and nutrients to a wetland for purposes of restoration. The particular wetland that is the subject of this assessment is known as the Central Wetlands Unit (CWU), encompassing about 30,000 acres, within Orleans and St. Bernard Parishes. This area was once a healthy baldcypress-water tupelo swamp that has been severely degraded over the last several decades, most notably by the construction of the Mississippi River Gulf Outlet (MRGO). The MRGO provided a direct channel for higher salinity waters to move inland from the Gulf of Mexico causing accelerated loss of wetlands. MRGO also provided direct access of surge from Hurricane Katrina resulting in breeches and overtopping of levees with consequential severe property damage and harm to the citizens of the area. Particular emphasis will be given to the public health aspects of the feasibility analysis. An evaluation of disinfection alternatives including: gaseous chlorine/dechlorination; hypochlorite/dechlorination, ultraviolet disinfection, ozone and ferrate technology will be presented. Ferrate is an innovative oxidant written as Fe which has an extremely high oxidation potential yet is considered an environmentally friendly disinfectant. Ferrate does not generate the potentially hazardous byproducts common to other oxidants and has been shown effective in removals of pharmaceuticals and personal care products (PPCPs) and endocrine disrupting chemicals (EDCs). Commercial scale applications, however, are limited. Results of the feasibility study conclude that the treatment facilities have or will have the necessary infrastructure to effectively treat the wastewater making it suitable for wetland discharge. It is recommended that current gaseous chlorination practices be modified to consider ferrate disinfection, hypochlolorite/dechlorination or UV as alternatives. A screening-level, qualitative risk assessment regarding human health and ecological factors of the wastewater effluent yielded no major concerns with the proposed project. It was recommended, however, that testing of effluents be conducted to assay potential concerns of PPCPs and EDCs. Some of this work is currently being conducted at Tulane and Xavier Universities and preliminary results are reported in the paper. The project was hence deemed feasible for implementation to restore and enhance these wetlands and re-establish cypress swamps which will significantly improve the environment and protect a significant portion of Orleans and St. Bernard Parishes from future storm vulnerability. A demonstration project has been funded by the New Orleans Sewerage and Water Board (NOS&WB) and has begun to define specific design criteria and expected performance in the study area.