Microbial Muscle
Strict environmental regulations, coupled with rising raw water costs, are making treatment and reuse of oily wastewater a necessity for many industrial and commercial operations. Manufacturing, machining, parts washing and vehicle wash industries continue to search for simple, cost-effective ways to treat and reuse their oily-water waste streams. While an abundance of water treatment systems are available today, many system operators remain frustrated by inconsistent treatment results and the often tedious and time-consuming operation and maintenance (O&M) requirements. However, a new generation of water recycle systems is taking advantage of biological product advancements and equipment innovations to provide adaptable, maintenance-free and cost-effective oily-water treatment for process water reuse. These unique systems are considered by many to be the ultimate solution for oily-water process effluents.
The Need
Stringent state and local regulations are putting more pressure on commercial/industrial process operators to find effective, easy-to-implement water treatment solutions that produce a clean, clear effluent for reuse and recycle within these processes. Over the past 10 years, states, counties and municipalities have taken an increasingly closer look at water consumption and discharge operations in the industrial sector. This scrutiny results from increased overall demand on existing municipal water systems, overtaxed wastewater treatment plants and a heightened awareness of potential contaminants (oils, greases, solvents, etc.) in wastewater discharges. In addition, regional droughts in many areas have spawned additional water consumption regulations that further restrict these operations.
Efficient biological degradation of petroleum is performed aerobically, requiring adequate aeration to sustain biological activity. |
For example, in August 1999 the state of New Jersey, which continues to experience a statewide drought, enacted water restrictions that required vehicle (car and truck) wash operators to pre-rinse with recycled water, shorten rinse cycles, reduce consumption and post signs to educate the public about water conservation. In 1997, the Pennsylvania Department of Environmental Protection restricted all industries from further groundwater discharge of process wastewater. In the past, discharge of certain regulated wastewaters to a "dry well" was deemed acceptable; however, concerns over oil, greases and solvents impacting groundwater prompted the new restrictions. For similar reasons, many municipalities across the country require pre-treatment for oily-water wastes, with significant fines for discharge volumes with high concentrations of total petroleum hydrocarbons (TPH), oil and grease (O&G), biochemical oxygen demand (BOD) and other solvent compounds.
Some remote facilities with oily-water wastes are not connected to sanitary sewer systems and must either use 100 percent reclaimed water or discharge process water directly to surface streams or impoundments. National Pollutant Discharge Elimination System (NPDES) permits regulate these releases to surface waters and usually impose very tight restrictions on oil and grease concentrations, pH, nutrient loadings and total suspended solids (TSS) content. Therefore, consistent and effective water treatment reclamation system at these facilities is essential.
The Past
Most facilities have tried traditional mechanical and chemical separation systems, such as oil/water separators, suspended solids filters and sedimentation/flocculation basins. These mechanical systems are subject to high failure rates because a large percentage of petroleum constituents are often emulsified and/or dissolved in the water stream and can pass through both oil/water separators and various filtration systems. The oils, greases and sediments build up over time, eventually fouling filter mechanisms, system nozzles, piping, pump impellers and other mechanical parts.
Chemical flocculation systems have also been used, with varying degrees of success. These systems use specific chemicals to coagulate and flocculate the organic particles, removing them from the waste stream. However, these chemical systems are extremely sensitive to pH levels, which often fluctuate widely due to varying concentration loadings and inconsistent process water flowrates. Therefore, chemical flocculation systems are often difficult to maintain and control, requiring an extremely high degree of operational and maintenance oversight - in other words, constant babysitting.
Biological treatment has distinct advantages over mechanical and chemical removal systems, including:
- complete degradation of both free and dissolved-phase oil and grease components within the water stream;
- removal of regulated nutrient compounds (nitrogen, phosphorus) from within process waters by utilizing it in the biological degradation process;
- effective odor control within storage/discharge systems through destruction of odor-causing organisms and contaminants;
- minimal day-to-day maintenance, providing low cost, consistent oily water treatment;
- elimination of the need for chlorine additives, which are dangerous and costly; and
- a high level of adaptability for use in conjunction with existing treatment systems, often as a pre-treatment or post-treatment polishing step.
The Future is Now
Biological treatment is the process of using bacteria and other biological enhancements under controlled conditions to convert organic compounds (in this case, oil, greases and solvents) to carbon dioxide, water and energy for cell production -- with absolutely no harmful byproducts or residuals. Efficient biological degradation of petroleum is performed aerobically, requiring adequate aeration to sustain biological activity. Additional critical requirements for any successful biotreatment process include a healthy compound-specific biological population, nutrients and a balanced pH environment.
The biological process eliminates not only petroleum, solvents and surfactant compounds, but also odor-causing bacteria, fungi and molds. |
Properly implemented biological treatment systems use activated, petroleum-specific bacteria and enzyme enhancements to remove oils, greases, nitrates and phosphates from the wash water stream. The enzyme enhancements act as catalysts for specific biochemical reactions, initiating contaminant breakdown and increasing bacterial degradation rates. The biological process eliminates not only petroleum, solvents and surfactant compounds, but also odor-causing bacteria, fungi and molds.
To highlight the applicability of biological treatment for oily-water production operations, the following case study summarizes a very successful biological treatment system at a rural commercial truck wash facility.
Biological Treatment at Work
BioShark Systems, a water treatment products and equipment vendor, recently installed a biological water reclaim system for a truck rental company. The facility is located in a rural community and does not have access to a sanitary sewer system. Trucks (up to 30 per day) are washed in a single wash bay using manual pressure wash equipment with an automatic final rinse bar. The used wash water flow of 15 to 20 gallons per minute (gpm) contains soaps, oil, grease and dirt removed from the trucks, which is collected in shallow drains and routed to an underground sump.
This site is regulated under an NPDES discharge permit that limits the levels of oil and grease, pH, phosphorus and total suspended solids (TSS) in the discharge stream (see Table 1).
Local regulations require an oil/water separator to reduce the oil and grease levels in the water stream. However, the previously installed oil/water separator system consistently failed to reach any of the NPDES permit limits.
The biological treatment reclaim system was installed to treat water within the sump and the oil/water separator, using extremely active petroleum-degrading bacteria and enzyme additives together with a powerful dual-media filtration system. The automated filtration system removed suspended solid particles over one micron and included an logic-controlled backwash system that automatically cleaned the filters when they became clogged with sediment.
After installation and operation of the biological reclaim system, these constituents decreased dramatically within the wash water discharge, as illustrated in Table 1. A biological system usually requires five to seven days to take effect. This lag period is primarily due to microbial acclimation and high existing contaminant mass within the water volume being treated. After start-up, the oil and grease or BOD levels remain consistently low due to constant scavenging of incoming O&G compounds by the established microbial community.
|
Compound |
NPDES Permit Limit |
Before Treatment |
After Treatment |
|
Oil & Grease (O&G) |
15 milligrams per liter (mg/L) |
30 to 165 mg/L |
0 to 6 mg/L |
|
Phosphorus |
1.0 mg/L |
14 to 77 mg/L |
0 to 0.5 mg/L |
|
Total Suspended Solids (TSS) |
50 mg/L |
100 to 300 mg/L |
10 to 50 |
|
pH |
6.0 - 8.5 |
8 to 10 |
7 to 8 |
Table 1 -- Results
These results were consistently achieved throughout the first 120 days of the project. Not only were the oil and grease, phosphorus and pH levels brought below NPDES permit limits, the system also significantly reduced odor problems associated with the underground sump chamber. The system discharged a clean, clear effluent with no odor, sheen or sediment. Currently, O&G and nutrient concentrations are non-detect, with TSS levels ranging from 10 to 50 mg/L. The automated filter backwash system has also reduced system O&M for the on-site wash technicians to simple monthly product re-supply and system checks.
Compared with a $30,000 to $80,000 cost for many mechanical water treatment systems, biological treatment can be extremely cost effective. |
Cost Comparison
The cost of a limited biological treatment system (an in-sump system without suspended solids filtration) ranges between $2,000 and $6,000 (initial capital investment), with a complete biological reclaim system (biological treatment, filtration, polishing) ranging from $20,000 to $30,000. Monthly costs range from $50 to $200 for product re-supply. Compared with a $30,000 to $80,000 cost for many mechanical water treatment systems, biological treatment can be extremely cost effective. In addition, the low O&M costs make it extremely affordable. As with any equipment purchase, the key to successful biological treatment and reclaim is an experienced, trustworthy vendor who can back their treatment system from installation through day-to-day operation.
Conclusions
A new generation of petroleum-specific biological products is making low-cost, low-maintenance oily water treatment a reality. These systems have proven results, produce high-quality effluent and can often be retrofitted to existing treatment platforms with very little effort. Biological treatment may be the best answer to your oily water wastes -- check it out.
E-sources
U.S. Environmental Protection Agency Office of Wastewater Management -- www.epa.gov/owm
Water Environment Federation -- www.wef.org
International Carwash Association -- www.carwash.org
American Petroleum Institute -- www.api.org
American Water Works Association -- www.awwa.org
Air and Waste Management Association -- www.awma.org
This article appeared in the July/August 2002 issue of Environmental Protection, Vol. 13, No. 7, page 34.
This article originally appeared in the 07/01/2002 issue of Environmental Protection.