Hydrocarbon and particulate contamination in wastewater is a well-known environmental hazard. Due to tightening environmental regulations, an ever-increasing source of such contamination in major cities comes from water collected from underground utility vaults and manhole water.
This contaminated water contains a smorgasbord of potential contaminants from transformers, groundwater and sewage ingress and street runoff water containing oils, gasoline, diesel fuel, lubricants, polychlorinated biphenyl’s (PCBs) and other hydrocarbons, as well as soluble and insoluble metals such as lead, mercury, copper, etc.
Prior to utility maintenance activity, the water is pumped out of these underground service and maintenance tunnels, and must be treated before being discharged back into the municipal sewer system. In many of these cities, the electric utility carries the responsibility for removal and disposal of the contaminated water.
It is not uncommon for the electric utility to collect the contaminated water and haul the untreated water to a third party for processing through a wastewater treatment system prior to final disposal. Although these companies are reliable and fully permitted to perform the required services, disposal costs can be high, upwards of $0.20 to 0.30 per gal.
Furthermore, if the third party becomes unavailable, for any reason, the consequences for the utility and its customers could be costly from both an environmental compliance and economic standpoint.
Need for control
As utilities further reduce manpower, the need for a simple, easy-to-use control system for automating a wastewater treatment system is increasing. Historically, PLC-based systems have been used to control such processes.
However, this requires specialized programming of the PLC for the particular process. Should any changes be required to the control strategy, it requires the end user to contract out a programmer to make these changes at an additional cost.
Furthermore, if remote communications for monitoring and control are required, the appropriate modules and specialized programming are also required. Thus, it is advantageous to be able to employ an off-the-shelf controller with built-in, easily changeable control strategies with integrated communications. One such device may be the Walchem WebMaster Series General Industrial Controller (WGI), developed and manufactured by Walchem Corp. This controller combines flexible, easy-to-use “Sensor-Control-Relay” mapping with a unique and patented communications technology, ShoulderTap “Server-On-Demand,” that leverages global communications standards. One example of the WGI’s use in monitoring and controlling involved the treatment of wastewater collected by an East Coast utility from manholes throughout its service territory.
A portable system was developed by JoDAN Technologies, Ltd., and constructed by Philip Services Corp. Equisol, LLC automated and integrated the system, selecting the WGI for its flexibility and versatility.
A different approach
Influent water is brought into the utility’s treatment system and first put through a series of large pore basket strainers.
From here, the water goes through a high efficiency inclined plane solids/oil/water separator to remove larger particles and non-emulsified oils. At this point, “gross” contamination is eliminated, and the water is collected in a surge tank prior to being put through a polishing process. The polishing process consists of gradient filtration followed by cartridge filters to remove any remaining hydrocarbons and then particulates down to levels within the permit limits so the water may be discharged.
An oil-in-water monitor on the final effluent water assures the water quality prior to collection and discharge into the municipal wastewater system. The entire process is monitored and controlled by the WGI controller. The treatment of the contaminated water may be either a continuous or a batch process. A vacuum truck filled with 3,000 to 4,500 gal of contaminated wastewater arrives at the treatment site and off loads into a weir truck. The process operates at approximately 30 gpm and runs automatically starting and stopping based on the influent water level in the weir truck.
Several parameters within the process are monitored by the WGI controller including: system flow rates, both total and instantaneous; water levels in both the raw water and clean water trucks; water levels in the separator and surge tank, oil level in the separator; differential pressure on the gradient filters; and the level of oil in water in parts per million.
Presently, the final treated effluent is captured in a collection truck that is sampled then trucked away for final discharge into the municipal sewer system. There are many safeguards in the process control system that ensure safe and efficient operation at the East Coast utility. The WGI will shut down the process should the water level in the weir truck get too low to avoid running the process dry. Likewise, the process is shut down once the collection truck reaches capacity to avoid overflowing the system. In the process itself, there are set level sensors in the separator that start and stop a rope oil skimmer. The system pressure is monitored to be sure there are no system failures or stoppages. The pressure differential across the filters are constantly measured and set to send an alarm when the filter needs to be changed. The system flow rate is measured to provide total throughput information. One of the most critical measurements is the hydrocarbon concentration measurement of the final discharge water. It is critical that preset compliance levels are not exceeded, and the hydrocarbon analyzer ensures proper operation of the skid. Should the hydrocarbon level reach a preset high level, the controller shuts down the systems and activates an alarm.
All of the process measurements are fed and logged by the controller. Interlocks are provided to protect the hardware and to ensure proper performance of the system. The controller at the East Coast utility not only provides easy to configure process control, but by making use of the broad communication capabilities of the system, the status of the process can be accessed in a variety of ways. Being Ethernet ready, the controller is a node on their LAN so anyone provided with the proper access code and password can see the current status and, if given the authority, can make configuration modifications to the process without the need for specialized programming skills.
The bottom line
The treatment system provides a highly functional process that effectively and efficiently removes hydrocarbon contamination from wastewater. The WGI controller provides a programmable system that can be tailored to the particular system.
In addition, user access to all environmentally critical data, 24/7 monitoring, alarm capabilities and data logging for compliance documentation, assure the customer of safe, effective operation. The result, a highly effective wastewater treatment system that is estimated to provide clean water for discharge at a rate of approximately $0.025 per gal.
“This system has been operating beyond expectations,” commented Philip D’Angelo of JoDAN, “The treated water is well within the compliance limits mandated by the utility’s discharge limits, at only a fraction of the cost previously observed. Additionally, the ability to remotely access historical data and system status, send out alarms and easily change control parameters assures that the operation runs smoothly, saves time and money, and most importantly, assures that the utility remains within the permit limits.”