There has been a steady increase in poultry processing rates over the fast few years. Unfortunately, this has led to a corresponding increase in wastewater pollutant concentrations. Although wastewater treatment has improved, stricter regulations of organic contaminants in wastewater has meant that many poultry processors have had to pay unnecessarily high fees for municipal water discharges.
One medium-sized processor, US-based Michigan Turkey Producers, decided to work with food manufacturer LycoManufacturing, to set up a patented, state-of-the-art screening system especially designed to improve the quality of the wastewater discharged by poultry processors.
Keeping down contaminant levels
Michigan Turkey Producers is a live turkey processor and boned meat company that makes US$100 million a year processing 4.5 million live tom (male bird) turkeys – around 20,000 birds per day. The average bird weight is about 40 pounds live and 34 pounds dressed, and 90% of everything the company does is boneless, with 60% of the meat going out fresh and 40% going out frozen. The greatest part of its distribution, about 70%, is in the mid-west US and East Coast with the remaining 30% going into Russia, Japan, China, Central America, Canada and South Africa. Its total facility is comprised of three buildings on 42 acres, with 375,000 ft2 of operations space and 187,000 ft2 for live-bird processing.
Like other processors, it has to keep a tight rein on the biochemical oxygen demand (BOD) and total suspended solids (TSS) levels in their discharged wastewater. Most processors do this by limiting poultry processing byproducts from entering and contaminating their wastewater stream, because of the difficulty in removing them prior to discharge. However Michigan Turkey is able to place fewer limits on the volume of particulate organic matter allowed to be put through their wastewater, because of the double screening system, which can remove sufficient load before discharge to leave levels of BOD and TSS well within municipal standards.
Relying on a screening system
“We purposely set up our wastewater system to handle anything that comes down it, any volume and concentration of particulate matter,” says Mike DeVries, plant engineer at Michigan Turkey Producers. “Consequently, we have a lot more load coming down our drains that we have to get out than other processors. This is different from how most poultry operations function, where usually they are trying to keep the load in their wastewater at a continually lower concentration throughout processing, because their screening system can't handle it. We are moving 700,000 to 800,000 gallons of wastewater a day through our system without any jam ups at the screening, and we are ending up with BOD and TSS ratings well within municipal standards.”
Like many food processing industries, poultry processing uses a great deal of water, particular for broilers. Five to ten gallons are used to process one five-pound, average-sized bird, and for turkey processors the volume of water used is considerably higher, since the average live weight of slaughtered turkeys exceeds 27 pounds. In some cases, bird weights can reach up to 40 pounds, with water consumption for processing in the range of 35 to 40 gallons per bird. A poultry processor can generate 750,000 to 1,500,000 gallons of wastewater daily.
This water is laden with proteins, fats and carbohydrates from meat, fat, blood, skin and feathers, along with grit and other inorganic matter. While waste load can be determined by a number of different measurements, including BOD, TSS, COD (the chemical oxygen demand), and FOG (fats, oil and grease), poultry plant wastewater is most often tested for BOD, a measure of the amount of oxygen needed to degrade the organic matter (feathers, fat and blood) in the wastewater.
Poultry processors are required to remove the majority of this organic material in their wastewater before discharging it from the plant in order to achieve compliance with local, state and federal environmental regulations. However, according to Lyco,few screening systems are capable of continuously cleaning out all of this material to a level within the standards of municipalities, and can ultimately lead to added charges and surcharges for wastewater dischargers.
“We discharge ultimately to a city municipal system and they charge us for anything that we put into the water,” says DeVries. “We have to control our loading costs to avoid additional surcharges.”
Dealing with screen blinding
The Double Drum screen provided by Lycouses rotary action to separate waste solids from liquids in one step, eliminating the need for two sequential, single-stage screens. Primary screening takes place when the wastewater enters the inner drum from the inside and screens out solids within the range of 0.06 inch to 0.02 inch. Secondary screening follows as the wastewater passes through the outer drum, screening particles as small as 0.02 inch.
“The Double Drum screen, which can handle up to 3,000 gallons per minute, was designed to eliminate the need for primary and secondary screening,” says Lyco'sTerry Brady. “Our research shows that in the majority of screening applications processors used a perforated primary screen then pumped the water to a secondary screen. Lycodesigned a way to do the primary screening with the inner drum screen first, and then the secondary screening done with the outer screen, which is the finer screen.”
The screen also has to deal with the issue of blinding, whereby the fats and other slimy-type particulates from poultry clog the screen openings. This is a common problem with traditional screening equipnent and can limit the volume of wastewater and load that can be moved through a screen and cause water and particulate to spill over the end of it. The Lycodouble-drum helps eliminate this problem by using a self-cleaning wedge-wire screen material, and a travelling spray system which can use as little as 10 GPM of fresh water to keep the screen open, compared to typical rotary screens that consume 36 GPM.
“A lot of other screen designs let material go through because they don't have the ability to manage it,” says De Vries. “Particularly when it gets into high volume quantities of material going through. This is not the case with the Lycodouble drum.”
There is also the issue of the processor's picking operation, where it drops right to water with the feathers, and the company actually moves the feathers via water.
“We had to have a Lycoscreen for that as well,” De Vries says. “The cost for us on the rendering side, or downstream side of processing, was the moisture content, so with the Lycodouble drum screen we found that we generate an extremely dry feather and consequently avoided any surcharging for moisture. That has been an enormous benefit all the way to the point that our rendering actually had to add moisture to process our feathers. The advantages are avoiding a surcharge, and also the advantage of being able to haul more volume with less weight.”
Poultry processors could have their rates reduced by a large portion using the double drum – such as a 40% charge reduction from municipalities, which could equal US$50,000 to well over US$100,000 in saving a year.
Approximately 84% of poultry processors in the US are using some form of screening application to reduce wastewater particulates - including internally-fed rotary screens, externally-fed rotary screens, and shaker-and-bar type screens. The vast majority of these are single-screen applications. With the advent of double-screen technology, processors can now capitalize on a much more efficient and cost-effective system for their wastewater treatment.
“I have been around a lot of screens used in the poultry industry, and have experienced their external and internal problems firsthand,” says De Vries. “I look for screening equipment that is heavy duty, durable, engineered to be user friendly, tool friendly and mechanic friendly. I want to be able to set it up and have it run with minimal maintenance. We have literally loaded the Lycodouble drum with thousands of pounds of product at different times and it has performed without any problems. Our need has been to get our heavily laden particulate out of the wastewater before we discharge it to the municipal system. The Lycoscreen manages that for us, particularly with TSS, which ultimately returns thousands of dollars back to us each month.”