Managing milk-plant odors by NJ Pinto PE, RA Straut PE, and EA Pond PE

O&M with UV disinfection by R Hill, PE and J Succow

Mitigating sewer odor and corrosion by RJ Pope, PE and N Ettele

Odor dispersion: models and methods by RJ Pope, PE and P Diosey, Ph.D., QEP

First step to effective odor control by RJ Pope, PE

Implementing a P2 program by BM Veith, PE

Featured facility: Kodak's King's Landing Plant by D Beecher, C Popen, D Taylor, D Wolf, R Regelsberger

People and places

NYSDEC notes

President's message by AJ Zabinski, PE

Executive Director's report: Leadership, what can it do for you? by P Cerro-Reehil

NYWEA scholarship fund by R Hennigan

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Summer 2000 — Vol. 30, No. 2

 

Mitigating sewer odor and corrosion

by Richard J. Pope, PE and Nancy Ettele

Quick reference
- Wastewater sampling program
- Results of investigation
- Development of alternatives

The Massachusetts Water Resources Authority (MWRA) has experienced nuisance odors and corrosion with many of its extension sewers. These lines convey wastewater from the locally owned and operated collection systems in the outer suburbs of Boston to MWRA treatment facilities. In particular, the Framingham Extension Sewer (FES) has troubled the MWRA for several years because it has prompted persistent odor complaints; the FES has also experienced pipe collapses and severe deterioration. The FES was constructed in the mid-1950s to convey wastewater from the Towns of Ashland, Framingham, and Natick to the MWRA's Nut Island Wastewater Treatment Plant.

Analyses used to ascertain source of H2S

The problems of odor and corrosion were attributed to high wastewater sulfide levels and the resulting generation of hydrogen sulfide gas (H2S). To address the problems, it was necessary to identify the source and extent of odor and corrosion in the FES and to develop alternatives to mitigate the wastewater sulfide. The MWRA did not know the source of the wastewater sulfide, whether it was being delivered from one or more of the towns' collection systems, or if it was being produced in the FES. MWRA began its search for the source of the odor and corrosion with an extensive investigation.

Wastewater sampling program

The presence and quantity of wastewater sulfide is important in understanding the cause and effect of odor and corrosion in the FES. The characterization of the wastewater for other parameters, however, was necessary to determine the relative strength and potential for the wastewater to support the biological activity that results in sulfide.

More than 250 sites in the FES and local collection systems were inspected to obtain baseline information. From this baseline data set, twelve locations were selected for a more comprehensive sampling and flow metering program that was designed to characterize the wastewater:

  • Major wastewater flows into the FES from the towns of Ashland, Framingham, and Natick

  • The start, midpoint, and end of the FES.

Automatic discrete bottle samplers obtained hourly samples during 24-hr periods, and daytime grab samples were collected for immediate analysis of other parameters. Continuous-recording atmospheric hydrogen sulfide (H2S) meters and continuous-recording flow meters were also installed at each location to characterize the manhole headspace and wastewater, respectively. Figure 1.

Sampling locations and their source and discharge relative to each other and the FES.

Samples were analyzed for several compounds including biochemical oxygen demand (BOD), sulfide, sulfate, pH, oxidation reduction potential, dissolved oxygen, and temperature. To obtain representative data, at least five sampling events were completed at each sampling location during 4-week field program.

Results of investigation

The data indicated the relative contribution of loadings from the three communities for wastewater sulfide and other parameters that promote the formation of wastewater sulfide and H2S. See table.

Table 1. Community wastewater contributions to the FES
Sampling location Sulfate (lb/day) Wastewater sulfide (lb/day) BOD (lb/day) Average flow (mgd)
Ashland        
2 3,723 9.48 1,986 0.876
3 15 0.28 252 0.133
Framingham        
4* 5,823 18.0 6,008 3.863
5 25 2.7 418 0.207
6 163 32.6 15,241 2.012
7 68 0.9 1,190 0.550
Natick        
11 34 0.24 350 0.196
12 711 2.73 3,679 1.374

*The loadings and flow attributed to the Town of Framingham.

These data and other findings from the study suggested the following:

  • The Town of Framingham was the most significant contributor of sulfate loadings to the FES at Location 6 and contributed more than half of the wastewater sulfide loadings to the start of the FES.

  • The Town of Ashland at Location 1 had significant wastewater sulfate loadings which appeared to be converted to wastewater sulfide in the local collection system and resulted in Ashland being a major contributor of wastewater sulfide to the FES.

  • The two locations that represented the majority of Natick's wastewater discharged to the FES did not show contributions that would significantly increase the sulfide loading in the FES.

  • The configuration of the FES promotes the release of odors at its start and at the one river siphon crossing.

Therefore, two of the three communities played a significant role in contributing to wastewater sulfide-related odor and corrosion in the FES. See Figure 2 for correlation of flow and H2S concentrations.

Figure 2. Comparative hydrographs: flow vs. H2S concentration (flow data for 7-23-97 — 7-24-97)

Development of alternatives

Next, the study had to determine not only how the sulfide-related issues could be mitigated but also who should implement the control strategies. Alternatives to mitigate the potential for corrosion and odor generation were based on strategies that included collection system improvements, chemical addition, and sewer headspace collection and treatment:

  • Improvements in the local collection systems to reduce the formation of wastewater sulfide, including more efficient pump station operation to reduce wastewater detention time in the collection system,
    • chemical addition to bind wastewater sulfide and prevent its volatilization, and chemical addition to prevent the conversion of sulfate to sulfide

  • Chemical addition to the FES and sewer headspace treatment at critical locations to control odor releases

  • Combinations of local system improvements and chemical addition.

Thus, this study identified both the source of odor and corrosion problems in the FES and the control strategies that could be implemented at the local level or in the FES. Currently, the MWRA is working out the details of implementation with the communities.
___________
Richard J. Pope, PE, is a vice president with Malcolm Pirnie, Inc. in White Plains. Nancy Ettele is a project manager with the Massachusetts Water Resources Authority.


 
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