Removal of Biological, Chemical or Radiological (BCR) Agents by Sorbent Addition and Gravity Settling at Wastewater Treatment Plants (WWTPs)

Introduction of biological, chemical or radiological (BCR) agents to a wastewater treatment plant (WWTP) via collect systems would be a relatively simple undertaking. While the adverse effect on human health and the environmental would depend on the type and concentration of the agent, the effect on public mental health would be significant. Responses need to be developed that can be used by WWTPs should such an event occur. Advanced technologies such as reverse osmosis, UV-oxidation, e-beam technology are capable of treating BCR agents but unless these technologies are part of the day-to-day operation of the WWTP their cost would be prohibitive (i.e., for use in response to an isolated BCR agent event). What are needed are economical and robust response methods that take full advantage of existing WWTP processes. In this research, the addition of solid sorbents (selected based on their ability to remove/treat BCR agents) to a conventional WWTP is proposed.

Consider a terrorist event in which a BCR agent is introduced to a WWTP via the collection system (a likely scenario given that major WWTPs will have heightened security). Following detection of BCR agent(s), either by sensing technology at the WWTP or through intelligence that the event had occurred, the WWTP would need to respond immediately given the plant's relatively short hydraulic detention time. In Figure 1, a simplified schematic of a typical WWTP is presented. Immediately after BCR agent detection the addition of the sorbent(s) would begin. The type(s) of sorbents used will be based on the type of BCR agent that was detected. Sorbent addition would occur prior to primary and secondary settling so that the settling tanks could be used to separate the sorbent from the liquid phase. Ideally, the vast majority of the contaminant would be removed in the primary settling tank so as to minimize upsets to the activated sludge system. Chemical and radiological agents would be removed primarily by sorption-type mechanisms while biological agents would be removed by a variety of mechanisms (e.g., sorption, entrapment by settling solids). Finally, if a BCR agent attack occurred, a large dosage of sorbent would most likely be used because of the seriousness of the situation thus, the ability of the settling processes to function adequately under high solids loadings must also be addressed.

In order to implement the proposed strategy effective sorbents must be identified, kinetic data must be generated, and the effect of solids loadings on settling and processes ascertained. Analogs that mimic the behavior of various BCR agents but do not have the associated health risks must first be identified.

Figure 1. Simplified Schematic of WWTP and Points for Sorbent Addition and Removal. Sorbent can be added prior to primary settling and the activated sludge (AS) process and removed in the settling tanks. AS recycle could be used to increase the contact time