Treatment with mineral oils and phenols using aquatic plants
Natural biological systems are becoming more widely used in the treatment of "difficult" wastewater containing phenols and hydrocarbons. The path was paved by studies funded by the US Army and the largest fuel companies 10-15 years ago. Now the US Military is gradually converting its facilities to plant systems, as well as Texaco Companies, Amoco and others.
We can assume that the need to please the institution and the public affects the choice, but the main causes are technical and financial. The biological systems are proven to be reliable systems that are efficient and cheap, in building and especially in maintenance, which is usually a weak spot. Natural biological systems can sustain severe fluctuation and function for years, without human intervention.
Several such systems were built in Israel by Ofra Aqua Plants for gas stations and two for the Air Force, systems that purify the wastewater from the engine workshops and the vehicle washing areas. The results speak for themselves. Not only do these systems function well in the difficult conditions and provide the high reduction percentages of hydrocarbons required by the regulation, but they also provide a significant reduction of variables that are not usually required in such cases, such as coliforms, without using chlorination.
At the Dead Sea Ahava factory, there also is a system built by Ofra over 15 years ago and functioning still, with no electricity, taking advantage of the rugged terrain instead of being hindered by it. The main problem there is oil emulsion, that clogged any previously installed system. The natural system operates without operating intervention, aside from periodic visits to thin out and refresh the vegetation. The system has become part of the "green" rebranding of the company and tours are performed for visitors who wish to see it.
Table 1. Average of two natural wastewater purification systems, with no electricity, installed by Ofra Aqua Plants at Israel Air Force Bases, purifying mixed industrial fuel depot water and sanitary sewage from workers facilities:
At a Dor Alon gas station in rural southern Israel, a comprehensive system was built in 2002 that treats car wash, fueling area runoff and sanitary wastewater. The system was designed to receive up to 4 cubic meters a day. In practice, due to increased traffic resulting from expanded roads, it received approximately 6 cubic meters and with further expansion of the station, up to 30 cubic meters a day! The treatment system was modularly expanded and adapted to the real input volume without affecting the day-to-day function. Notwithstanding the fluctuations in volume, throughout the years that the system has been active, it has been monitored regularly, never showing abnormalities, with one exception - in Passover 2005. During the week-long holiday there were over 2,000 visitors a day. Due to the excessive amount, the system was monitored after the holiday. The system managed to deal with the excess load, and not only did it not collapse but also produced good quality water. The only measure that was slightly above standard was biological oxygen consumption, that was at 39 mg/L, compared to normally <2-20 mg/l.