Prior to finding ProChem, this wood products manufacturer had been working with their local publicly owned treatment works (POTW) to treat their water. They needed to lighten their heavily pigmented water so that it could be penetrated with a UV light in order to disinfect it before discharging to the POTW.
The company initially hired an engineering firm to find a solution, but because there are so many nuances in wastewater treatment that require expertise in multiple disciplines, they were unable to provide one. They would have needed to understand the wastewater, the chemistry, and the unique needs of the customer -- a specialized set of services they turned to us to provide.
The plant's wastewater comes from their wet electrostatic precipitator (WESP) system, which uses water and electricity to scrub fine wood particles from gases before they can be released into the atmosphere according to EPA regulation. Those fine wood particles end up in the wastewater that the ProChem system needed to treat. Our starting point was our CleanWESP water treatment program, designed by ProChem chemists specifically for the wood products industry to protect valuable equipment such as the WESP. Even with this solution in place, this customer had significant problems that would require some creative problem-solving. Fortunately, our team lives by the premise, "The bigger the problem, the bigger the solution."
While ProChem's experts were researching the problem, the POTW continued to tighten their restrictions. As a result, the scope of the project pivoted from merely lightening the pigmented water for discharge to treating and reusing 10% of their wastewater inside the plant. This is what we refer to as a "kidney loop" -- continuously treating part of the stream, rather than the whole thing, to keep the whole stream cleaner.
ProChem's custom-tailored solution to treating wastewater for discharge while also implementing water reuse required a carefully orchestrated combination of chemistry, equipment, and technology.
The Chemistry
When dealing with wood wastewater, there's only one proven chemical treatment that works. A coagulant turns dissolved contaminants into solid particles, while the polymer holds those together to make bigger particles, which typically sink to the bottom. But in cases such as this, the wood particles float. The chemistry team at ProChem had to find a combination of polyamene, pH, coagulant, and polymer that had good separation to allow the solids to float in as compact a layer as possible and also produce water as clear as possible. At the plant, the particles on the top get skimmed off and go to the belt press, where the water in the sludge is removed and the sludge is disposed of.
The Equipment
The system that ProChem designed includes pretreatment, sand filtration, reverse osmosis membrane filtration, and UV lights. The system is based around a specialized chemical treatment program coupled with I-PRO™ and B-PRO™ membrane technologies. Designed to treat up to 60,000 gallons per day at 200 gallons per minute (gpm), the current system handles 125 gpm of reuse water and is integrated with existing clarifiers, dissolved air flotation (DAF), and a belt press.
ProChem fabricators constructed three Conex containers at our facility in Elliston, Virginia, and outfitted them with amenities for 24-hour, year-round operation -- lights, heaters, fans, and ventilation.
One container houses three 62-ft3 sand filters operating in parallel with one in service at a time. The sand filters are equipped with automatic switching and backwashing of exhausted columns using permeate water.
Our membrane technology for this project included both I-PRO and B-PRO Conex containers. Both containers consist of an automatic prefilter switching to reduce down time, additional chemistry to prevent scaling and biological growth, and an automatic phase change based on conductivity -- keeping discharge within operating parameters. The I-PRO container consists of 10 membrane housings, each with six membranes, while the B-PRO container has eight membrane housings with four membranes in each.
As always, we incorporated the most up-to-date technology that was appropriate for the customer's particular needs:
- High-efficiency booster for maximum reuse
- 125-hp motor and operating pressure, producing approximately 700 psi to 900 psi in the I-PRO
- 50-hp motor with an operating pressure between 300 psi and 400 psi
The initial walkthrough at the customer's plant revealed tight spaces that would require precise piping work to create the most efficient and sustainable system. For a clean piping sequence, our Project Superintendent made sure there were no "jumping pipes," meaning no pipes overlap. Overlapping diagonal pipes make the system less serviceable. For example, simply fixing a valve could require cutting pipes. Because of our close attention to detail, that wouldn't be necessary for this project.
The Technology
This system is automated and continuously transmits data to ProChem's AutoRun™ software. To accomplish this, our Controls & Instrumentation Engineer used the P&ID to determine how many PLC (programmable logic controller) inputs and outputs would be needed. The PLC is at the center of the control system, continuously monitoring the state of input devices and making decisions based upon a custom program to control the state of output devices as much as 100 times a second.
Our Controls & Instrumentation Engineer writes custom programs using algorithms to monitor flow, dose chemicals, adjust pH, control agitator speed, and much more. Any signal that can be measured can also be manipulated.
ProChem upgraded the customer's wastewater treatment system to provide operators the means to enhance their process for meeting the plant's water quality needs. As part of the upgrades, ProChem modernized the control system utilizing a Remote I/O solution. This technology reduced wiring costs while improving operational readiness and reliability.
The Remote I/O system provides a reliable method to transfer monitoring and control signals to and from the PLC-based control system. In this configuration, two Remote I/O stations are situated along the Ethernet network in different areas of the system. Each station contains five to 10 I/O modules. For monitoring applications, the system collects signals from analog transmitters or discrete devices. It concentrates the signals and, when polled by the network master, sends them over the Ethernet network directly to the main PLC control panel. For control, process commands from the host are transmitted over the network and converted to analog or discrete form to control valves, pumps, motors, and other types of proportional and on/off control elements.
The Takeaway
This wood products manufacturer has a large and complex treatment system with multiple moving parts. The challenge for us was to make all those parts work together in balance. It was the most complicated control system our engineers have ever designed.
As always, we maintain an ongoing relationship with this customer and continue supporting them both remotely and on-site. In fact, one of our Environmental Technicians is responsible for the day-to-day optimization of the system.
ProChem's team took a customer who was discouraged and gave them the solution they needed to protect their costly (about $1 million/year) WESP equipment by treating and reusing their wastewater. The remaining wastewater is discharged to the POTW, guaranteed to maintain compliance.
