Clean and Clear
Strict environmental regulations coupled with rising raw water costs are making treatment and reuse of oily water wastes 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 wastes. 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 water treatment for process water re-use. 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 re-use 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. Furthermore, regional droughts in many areas have spawned additional water consumption regulations that further restrict these operations.
Over the past 10 years, states counties and municipalities have taken an increasingly closer look at water consumption and discharge operation in the industrial sector. |
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 pretreatment for oily-water wastes, with significant fines for discharge volumes with high concentrations of total petroleum hydrocarbons (TPH), oil and grease (O&G) and other solvent compounds.
Some remote facilities with oily-water wastes are not connected to sanitary sewer systems, and must use either 100 percent reclaimed water or discharge process water directly to surface streams or impoundments. The 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, a 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, filters and sedimentation/flocculation basins. These mechanical systems are subject to high failure rates because a large percentage of petroleum constituents (often emulsified or dissolved in the water stream) and sediment can pass through an oil/water separator and/or pre-filter. The petroleum and sediment builds up over time and eventually fouls filter mechanisms, system nozzles, piping, pump impellers and other mechanical parts.
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. |
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 chemical concentration loadings and inconsistent process water flowrates. Therefore, chemical flocculation systems are very 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: 1) complete degradation of both free and dissolved-phase oil and grease components within the water stream; 2) removal of regulated nutrient compounds (nitrogen, phosphorus) from within process waters by utilizing it in the biological degradation process; 3) effective odor control within storage/discharge systems through destruction of odor-causing organisms and contaminants; and 4) minimal day-to-day maintenance, providing low cost, consistent oily water treatment.
The Future of Wastewater Treatment
Biological treatment is the process of using bacteria and other biological enhancements under controlled conditions to convert organic compounds (in this case, oil, greases, solvents) to carbon dioxide, water and energy for cell production -- with absolutely no harmful byproducts or residuals. The main requirements critical to any successful biotreatment process include an active, healthy compound-specific biological population, oxygen, nutrients and a balanced pH environment.
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 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 sanitary sewer hookup. A single wash bay includes manual pressure wash equipment with an automatic final rinse bar. The used wash water - containing soaps, oil, grease and dirt removed from the trucks - collects in shallow drains and is routed to an underground sump.
This central facility washes up to 30 trucks per day (average wastewater flow of 15-20 gallons per minute (gpm)), and the wash water requires treatment prior to discharge to a surface stream. This site is regulated under an NPDES discharge permit which limits the levels of oil and grease, pH, phosphorus and TSS in the discharge stream. The NPDES cleanup criteria for this wastewater is included in 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 for removal of suspended solids particles over five microns. After installation and operation of the BioShark biological reclaim system, these constituents decreased dramatically within the wash water discharge, as illustrated in Table 1 and graph.
|
Compound |
NPDES Permit Limit |
Before Treatment |
After Treatment |
|
Oil and Grease (O&G) |
15 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 40 |
|
pH |
6.0 - 8.5 |
8 to 10 |
7 to 8 |
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 new system discharged a clean, clear effluent with nondetectable odor or sheen. Currently, O&G and nutrient concentrations are non-detect, with TSS levels ranging from 10-20 milligrams per liter (mg/L). The automated filter backwash system has also reduced system O&M for the on-site wash technicians to simple product re-supply and flipping the On/Off switch.
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 and sediment filtration) ranging from $20,000 to $25,000. Monthly costs range from $50 to $200 per month 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 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.
This article originally appeared in the September 2001 issue of Water & Wastewater Products, Volume 1, Number 2, page 50.
This article originally appeared in the 09/01/2001 issue of Environmental Protection.