Tools for Considering lndustrial User Discharges and the Impacts to Treatment

Authors:

  • Brandt Miller, Chamindra Dassanayake, Joseph Rohrbacher - Hazen and Sawyer
  • David Ornelas - El Paso Water

Introduction / Background

El Paso Water (EPW) provides water, wastewater and storm water services to the City of El Paso, Texas. EPW owns and operates four wastewater treatment facilities across the city including the John T. Hickerson Water Reclamation Facility (WRF), Haskell R. Street Wastewater Treatment Plant (WWTP), Roberto R. Bustamante WWTP and the Fred Hervey Water Reclamation Plant (WRP), treating, in total, 60 million gallons per day (mgd) on average. This presentation focuses on the John T. Hickerson WRF (JTHWRF), which serves residential and industrial customers to the west and northwest of downtown El Paso. JTHWRF is permitted to treat 17.5-mgd annual average flow and up to 35-mgd peak 2-hour flow.

The JTHWRF began experiencing process stresses due to increased levels of biochemical oxygen demand (BOD5) in the Spring of 2015 in addition to accumulation of “yellow grease” occurring in the collection system. EPW determined that the two observations coincided with a new significant industrial user (SIU) began discharging to the collection system. Hazen performed onsite bench scale testing to determine the potential toxicity of the industrial waste as well as the impacts to ammonia removal rates and carbon oxidation rate limitations. Hazen then developed a whole plant process simulator using BioWinTM 4 (Envirosim, Ltd.) software to further evaluate the industrial waste impacts across the entire plant including solids production, aeration and treatment capacity. In addition, Hazen evaluated multiple wasting strategies for the SIU, potential BOD5 limits for pretreatment and relative cost of treatment under each scenario.

Purpose

The purpose of this presentation is to demonstrate the benefits of using whole plant process models to determine impacts from potential SIUs (sludge production, aeration, nutrient limitations, overall plant capacity, etc.), establish pretreatment discharge limitations and quantify the additional cost to treat industrial streams to help establish discharge loads.

Results and Analysis

The following results are some examples of what the process modeling and analysis revealed and will be discussed in more detail during the presentation.

  • The influent BOD5 load increased by approximately 50% due to the industrial waste.
  • Prior to the industrial discharge the plant was operating at about 45% of design capacity. The addition of the estimated industrial waste increases the influent BOD loading above the original design load, potentially reducing the plant’s capacity by more than 35%.
  • The additional industrial load would double aeration demand and increase sludge production by approximately 80%.
  • The process model was used to determine a limit on BOD5 load from the industrial user to maintain the plant’s treatment capacity in addition to a load that would not significantly impact the existing operations.
  • More detailed assessments were made to determine potential wasting strategies during lower influent BOD5 load periods based on the diurnal load patterns (without the industrial waste) and resulting impacts to aeration demand, sludge production and treatment efficiency.
  • The cost of treatment was evaluated and compared to other municipal wastewater utilities to determine changes required to the ordinance.

Conclusions:

The process model and bench scale testing allowed EPW to quantify the impacts from accepting the industrial load without pretreatment, identify capital improvements and estimate operation costs associated with treating the industrial load and understand multiple options for the industrial discharge.

This tool provided EPW with the confidence needed to justify costs to treat the waste through JTHWRF or pretreatment options that could lower the costs to treat through JTHWRF. These costs were compared to EPW’s SIU surcharge ordinances and to other utilities in the state to determine the best wasting strategy.

For more information, please contact the author at bmiller@hazenandsawyer.com.

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