Final Report: Development of a Cost-effective, Nutrient-removal, Onsite Household Wastewater Treatment System for Environmentally Fragile Areas

EPA Contract Number: EPD14026
Title: Development of a Cost-effective, Nutrient-removal, Onsite Household Wastewater Treatment System for Environmentally Fragile Areas
Investigators: Cid, Clément A
Small Business: Caltech Lab for Energy and Water (CLEW)
EPA Contact: Richards, April
Phase: I
Project Period: May 1, 2014 through April 30, 2015
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2014) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Wastewater and Sustainable Infrastructure

Description:

The purpose of this EPA SBIR Phase 1 was to develop a cost-effective onsite nutrient removal system from household wastewaters in environmentally fragile areas. At the core of the CLEW System’s technology lies an electrochemical reactor with multilayer semiconducting anodes and stainless steel cathodes developed at the California Institute of Technology by Prof. Hoffmann and his team. This electrochemical treatment technology oxidizes chloride into active chlorine to disinfect the wastewater, and it reduces its chemical oxygen demand and removes its nitrogen content.

Summary/Accomplishments (Outputs/Outcomes):

The main objective of Phase I was to address effectively the nitrogen and phosphorus removal from the system’s effluents to comply with drastic TMDLs of 5 mg/L for nitrogen and 1 mg/L for phosphorous.

 
The objective of the Phase I development plan for nitrogen removal was to promote nitrogen and phosphorus removal with a minimum addition of NaCl in the household effluent by using the household wastewater treatment system, which has already been developed. This is done while maintaining disinfection, chemical oxygen demand (COD) removal and dehydrated sewar sludge (DSS) removal at acceptable levels.
 
CLEW Systems used different media to simulate household septic tank and toilet sewage in its laboratories:
 
  • Decanted toilet wastewater from the self-contained prototype installed at the California Institute of Technology (Pasadena, California) mixed with direct household effluent from Los Angeles County Wastewater Reclamation Plants (Whittier, California).
  • Direct household effluent from Los Angeles County Wastewater Reclamation Plants (La Cañada, California and Whittier, California).
  • Water and urine from one healthy individual (26-year-old male).
 
The company decided to first investigate the direct electrochemical treatment of the household effluents. By doing so, it can limit the installation cost and operation cost to a single electrochemical system. Furthermore, the level of suspended solids in the septic tank leachate usually does not require the use of an electrochemical coagulation-flotation step to remove these suspended solids since anaerobic and decantation processes happen naturally in the septic tank. Only a nitrogen- and phosphorus-removing step is necessary.
 
An important parameter in any electrochemical process is the ratio of the surface area of the electrode to the volume of the liquid in contact with this electrode. This ratio determines the optimal coulombic efficiency (i.e., the best usage of the electrons to drive the desired chemical process: removal of nitrogen and/or phosphorus, in this case). This ratio was studied in urine and water mixtures to determine the best size of the electrochemical reactor and the findings are presented in Figure 1.
 
 
Figure 1: Nitrogen removal efficiencies for different volume-to-surface-area ratios r (triangle r = 0.03, cross r = 0.06 and diamond r = 0.09) and different urine concentration (green 20%, purple 35% and red 50%). Original nitrogen concentration in urine was 4200 mg N/L (+/- 150 mg/L, depending on the sample).
 

Conclusions:

A system that electrochemically removes nitrogen at the source needs to be designed so that the electrode surface area to reactor volume ratio r is as low as possible. Obviously, the volume of liquid waste to treat and the size of the treatment system are limiting, but for a single toilet with four users the size of the system would not be bigger than 20 L (less than 8” × 4” × 4” box).

The company’s original submission for the design consisted of a septic tank replacement unit. The phase 1 research shows that this method is too expensive, due to treatment capacity and necessary NaCl levels.
 
Commercialization: CLEW Systems has an ideal commercialization partner in mind that has the exact right distribution and manufacturing specialties for the technology.

Supplemental Keywords:

Wasterwater treatment, energy efficiency, solar powered wastewater treatment, alternative septic sytem, water reuse