Heavy Industry Plant Wastewater Treatment, Recovery ang Recycle Using Three Membrane Configurations in Combination with Aerobic Treatment

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Courtesy of Water Environment Federation (WEF)

ABSTRACT
In the late 1990’s a major diesel engine manufacturing plant began evaluation of wastewater treatment technologies that would improve the quality of wastewater discharge, would produce treated effluent of reduced oil and grease, BOD and COD load suitable as feed to their sanitary waste biological treatment plant, and eliminate the costs and risks associated with the use of hazardous chemical/physical treatment chemicals used to traditionally treat industrial waste. Several waste management options were examined, including waste reduction via production modification within the plant, pointsource, and end-of-pipe membrane separations technology. This study led to the commissioning of a UF (Ultrafiltration) pilot study using full scale membrane modules with the objective of economically specifying the correct membrane type and configuration to reduce oil and grease, suspended solids, and total solids contaminants. It was found, based on cost, technical, and operating (labor, chemical cost, variability in effluent quality) considerations, that UF met those objectives.

The commercial scale membrane system specified was an open-channel tubular UF system. Permeate off the UF contains less than 30 mg/l oil and grease, less than 0.5 mg/l Cu and Zn, and less than 10 mg/l suspended solids.

In 2005, with increased water demand in the plant, and pressure from the authorities to rduce water usage, additional membrane systems (UF and RO) were designed and installed as post treatment to the activated sludge process for recovery and recycle of wastewater back into the plant. The UF system is a hollow fiber configuration. The RO design is spiral wound membrane. This paper describes the performance of membrane systems of three configurations. Productivity, filtrate quality, and operating costs on this installation are presented and show that membrane filtration, in combination with biological treatment, is an economically viable and accepted technology for closing the loop and recovering water for reuse in heavy industry facilities.

INTRODUCTION
The metalworking industry can be a major consumer of water. Water is used for processing, cutting and machining, and for cleaning raw materials and parts used in engine fabrication. Typically the wastewater portion from an engine production process contains:

  • Suspended Solids
  • Settleable Solids
  • Fats, Oil, and Grease
  • Petroleum Hydrocarbons
  • Heavy Metals
  • Biological Oxygen Demand
  • Chemical Oxygen Demand
  • pH swings
  • Microorganisms

These constituents of oily wastewater are at levels unacceptable for direct discharge to sewer so they are treated on site, or hauled away for treatment by others.

Membrane systems are designed to treat waste to significantly reduce the volume of concentrate that is hauled away from the plant. Ultrafiltration systems produce an effluent that is low in fats, oils, grease, metals, and suspended solids allowing direct discharge to the drain. An ultrafiltration membrane can reduce BOD by up to 90-95%, suspended solids to < 5 mg/l, oil and grease to < 50 mg/l, and true petroleum hydrocarbons to <10 mg/l. Heavy metals, once precipitated by hydroxide precipitation, are typically measured in the 0.5 mg/l range. The permeate from an ultrafilter is
sometimes further treated with reverse osmosis membrane if additional reduction in TDS, BOD or COD is required. RO permeate is of such high quality in these cases that often it is saved and reused in the plant rather than wasting it to drain. These membrane systems operate from 7 to 14 days or more without cleaning and can result in as much as 90% of the waste water being converted to water suitable for recycle.

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