A Comparative Cost Analysis of Wastewater Treatment Between Constructed Wetlands in Beaumont, Texas and a Conventional Treatment System in Galveston, Texas

Chad Boshers1, Harrison McNeil1, Jade Wallace2 (Faculty Advisor: Dr. Jae-Young Ko) 1. Ocean and Coastal Resources, Texas A&M University 2. Marine Biology (minor: OCRE), Texas A&M University

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Introduction

Results

Conclusion A constructed wetland is an artificial wetland designed to utilize the natural processes (microbial, biological, physical, and chemical) of wetland and aquatic plants to treat wastewater. Constructed wetlands have been used for the tertiary treatment of municipal, industrial, agricultural, and livestock wastewater since the 1990’s due to their low cost and maintenance requirements. These densely vegetated systems can effectively treat organic matter, such as nitrogen and phosphorous, as well as decrease concentrations of heavy metals, organic chemicals, and pathogens. Previous studies have shown constructed wetlands to have uptake rates of 80-90% of organic substances. The activated sludge process is a conventional primary and secondary wastewater treatment process that uses aeration and complex microbial communities. These systems are efficient in removing organic materials, but result in large amounts of excess sludge as byproducts. Conventional wastewater treatment begins with a coarse debris screening (e.g., leaves, tree limbs, branches) and then a sand and grit removal process. After fine sedimentations are filtered out, the wastewater undergoes primary clarification; the sludge produced sinks down into the sludge digesters for solid disposal and the liquid is passed into the secondary stage of treatment. There are two kinds of treatment the clean water can undergo; Attached Growth Process (AGP) or Suspended Growth Process(SGP). The City of Galveston plant used an SGP process. During this stage, the wastewater goes through an aeration process that speeds up the work of aerobic bacteria and other microorganisms that break down the organic matter. A second clarification process occurs next and remaining sludge is pumped back into the aeration phase to assist with the SGP. The clarified water is disinfected with chlorine, dechlorinated, and then filtered out into Galveston Bay. The City of Beaumont plant had a near identical process with the exception of the secondary phase of treatment; instead of an SGP, it uses an AGP, where a fixed film is grown on the surfaced of stones forming a microbial growth on the media. The wastewater passes over the growth which provides the water with oxygen while the bacteria consumes the organic matter as food. The objective of this research is to describe the different mechanisms of the two different wastewater treatment methods and to conduct a comparative cost analysis in order to quantify the benefits of wetlands over conventional systems. We aim to show the benefits of utilizing natural ecosystems by comparing the annual operation costs of the Beaumont and Galveston facilities.

Methods Using the information collected from a current wastewater treatment system in the City of Galveston (NPDES permit # TX0027791), and from the constructed wetlands facility in Beaumont, Texas (NPDES permit #TX0046990), we analyzed the water quality changes of the two wastewater treatment facilities, and determined how much money is spent on the facilities annually. The annual operation costs per MGD (million-gallons-per-day) of the two facilities were estimated also. We then compared these values to the cost of a constructed wetland’s money usage to find which of these two waste water management strategies has the more attractive method of cost cutting.

This figure shows a model of the constructed wetlands

system such as that in Beaumont. The two major

differences from the activate sludge system is the use of

trickle filtration, and the tertiary filtration using the

wetlands.

The activated sludge system, like Galveston’s plant lacks tertiary filtration. It also uses aerator tanks as opposed to trickle filtration.

Galveston Beaumont Wastewater volume

(MGD) 1.8 21

Water Quality Influent Effluent Influent Effluent

BOD (mg/L) 99.6 2.8 131.0 5.0 NH3/N (mg/L) n/a n/a 31.7 3.9

TSS (mg/L) 95.0 4.0 395.0 22.0 DO (mg/L) 2.7 7.1 5.0 7.4

Facilities Galveston, TX Beaumont, TX

Engineering methods Clarifier/activated sludge trickle filtration/

constructed wetlands.

Annual operational budget $855,714 $2,300,000

Annual Operations and Maintenance Cost per

MGD $462,548 $111,004

Through a cost analysis of the constructed wetlands system in Beaumont and the activated sludge plant in Galveston, we found that tertiary filtration using constructed wetlands is significantly less expensive than the traditional method. The annual operational and maintenance cost of the Beaumont plant is only $111,004 per million gallons filtered, as opposed to $462,548 for the Galveston plant activated sludge system. Further, the Beaumont wetlands systems has contributed to the restoration of natural ecosystem and is used for environmental education. After consideration the economic and non-economic benefits, the constructed wetlands should be significantly considered as a component of wastewater treatment system.

Table 1. The typical wastewater volume treated and the water quality changes of both Galveston and Beaumont facilities

Table 2. A comparison of annual operational costs