Advancing pet food manufacturing wastewater

Many of us rely on pet food manufacturers to provide high-quality and nutritious food products that keep our pets happy and healthy. As part of this process, pet food manufacturing facilities must render and blend animal proteins, vegetables, grains and other organic ingredients to produce wholesome, well-balanced wet and dry food products. In doing so, however, pet food manufacturing plants inevitably generate wastewater with high levels of contaminants. These compounds include total suspended solids (TSS), organic compounds (BOD/COD), ammonia (NH₃-N) compounds, and fats, oils and grease (FOG) — all of which can significantly impact ecosystems and public health if not properly treated.

Given these factors, developing an effective solution to treat wastewater prior to its reintroduction to the environment is critical. At the same time, it is not always a clear-cut process, requiring the right combination of physical, chemical and biological processes rather than a one-size-fits-all solution.

To help select the best wastewater treatment plan for pet food manufacturing applications — whether to meet local pretreatment regulations or promote more sustainable treatment practices — this article provides a helpful overview of the types of contaminants encountered and describes the different solutions available to ensure pet food manufacturers achieve required effluent regulations. It will also explore integrated wastewater technologies that not only effectively remove the contaminants, but also offer cost, energy and performance advantages.

Stay ahead of evolving standards

Whether to meet U.S. EPA standards or state or local effluent requirements, pet food manufacturing plants need to monitor and report both the quantities and types of generated waste. While the EPA sets national standards, state and local governments may impose different pretreatment standards, with regulations varying based on a facility’s size and where it discharges wastewater.

All of these regulations are subject to change over time. To ensure compliance and environmental protection, it is important to stay as up to date as possible on the latest regulations and best practices — whether at the federal, state or local level.

The role of water in pet food applications

Pet food manufacturing facilities require water for many operations on the production side. For example, water is used to mix and combine ingredients to create the proper consistency, as well as in the baking processes. Water also plays a role in sanitation for cleaning equipment, machinery and production areas, preventing contamination.

The wastewater generated from these and other processes must be properly treated to comply with increasingly stringent environmental regulations. Effluent regulations, for example, limit the amount of pollutants — including biochemical oxygen demand (BOD), TSS, ammonia, total nitrogen and phosphorus — that are discharged to a privately owned treatment works (POTW) or directly into bodies of water in order to prevent contaminants from harming aquatic life and degrading water quality. Treating wastewater from these applications also prevents the spread of harmful pathogens.

It is important to be familiar with the specific contaminants present within pet food wastewater — and the technologies that offer solutions to these challenges — in order to design the optimal treatment solution. What follows is an overview of common treatment methods that may be used in pet food wastewater treatment.

Physical separation methods

Physical separation methods are the first step in treating pet food manufacturing wastewater — specifically, removing FOG, TSS and particulate BOD/COD. This method is a simple and cost-effective way to remove a large portion of these pollutants. A dissolved air flotation (DAF) system — one such separation technology — removes FOG, TSS and non-soluble organics by dissolving pressurized air into water and forming tiny microbubbles. As these bubbles enter the flotation zone located within the DAF system, contaminant particles attach to the bubbles, lowering the particle density and causing the FOG, TSS and other non-soluble organics to separate from the wastewater and rise to the surface. The top surface layer of separated contaminants is then skimmed and collected into a sludge hopper.

A new DAF system from WWW has lowered a pet food manufacturer’s operating costs and expanded wastewater treatment demands.

Improving wastewater treatment capacity with Ideal DAF

Not all DAF systems are created equal. The best ones — such as the World Water Works (WWW) Ideal DAF — have a compact design, low operational chemistry and low energy costs, with high removal efficiency. Here is how it works, along with how it improved one pet food manufacturer’s wastewater treatment capacity.

Ideal DAF features a cross-flow design that facilitates lower water velocities and better solid separation. To optimize the treatment process, the influent header has multiple injection points, allowing the introduction of whitewater — a highly saturated pressurized stream of air and DAF influent that includes a polymer flocculant. Ideal DAF also has a cone-bottom design for easy settled sludge removal.

At WWW, we recently upgraded a Nebraska-based pet food manufacturer’s DAF system to improve the plant’s wastewater treatment capacity. At the time, the plant’s aging stainless steel DAF system could not meet new treatment demands for TSS, FOG and insoluble BOD particulate matter. We designed and built this new system to provide two times greater treatment capacity while reducing energy consumption with the WWW dissolved air generation (DAG) system.

The WWW DAF system was designed at a flow rate of 120 gallons per minute and was delivered to fit into a footprint similar to that of the prior unit, facilitating installation and freeing the manufacturer from having to make physical adjustments to equipment. Thanks to its polypropylene construction and zero moving parts below the water’s surface, the new DAF system endures the harsh operating conditions with minimal maintenance. Since its implementation, the new unit has lowered the pet food manufacturer’s operating costs while meeting expanded wastewater treatment demands.

Biological solution methods

In addition to FOG, TSS and non-soluble organic compounds, the wastewater in pet food manufacturing plants contains high levels of soluble biological contaminations like BOD/COD, ammonia-nitrogen (NH₃-N) and phosphorus (PO₄-P).

In order to meet effluent limits for these soluble parameters, one popular treatment method — known as the activated sludge process — uses bacteria to treat the pollutants contained in the wastewater. These microorganisms consume organic matter, nutrients and other contaminants within the wastewater, producing carbon dioxide, water and biomass as they grow. The digested wastewater flows to a secondary clarifier for sedimentation of the bacteria, which then return to the head of the aeration tank while the clarified water is discharged.

Another biological treatment method to reduce soluble parameters uses a moving bed biofilm reactor (MBBR) process, which is a fixed-film system that reduces BOD and enables nitrification and denitrification. This technology relies on specially designed bio-media within the MBBR tank that enables bacterial growth. These biofilms digest the organic matter in the wastewater and convert soluble material into biomass that can be removed downstream. Near the top of the tank, a stainless steel sieve allows water to exit the reactor while preventing the bio-media from escaping. Compared to conventional activated sludge systems, MBBR is a flow-through system that reduces operator attention. It also reduces the equipment footprint due to its high effective surface area provided by the specially designed bio-media in the system.

Exploring Ideal MBBR

WWW Ideal MBBR has one of the smallest footprints in the industry and features excellent tolerance to load swings and temporary load deprivation. A stainless steel aeration manifold, installed at the bottom of the aerobic reactor, provides the dissolved oxygen for BOD removal and nitrification. Different bio-media is employed in an anoxic environment for denitrification applications, as well as specially designed media for only nitrification. This system is highly resilient, simple to operate, requires low capital investment and can easily retrofit existing systems.

Phosphorus removal methods

Finally, if phosphorus must be removed from the pet food manufacturing wastewater before it is released into the environment, adding coagulants to the wastewater to precipitate the phosphate is a solution. Similar to the removal of suspended solids using DAF technology's physical-chemical processes, phosphorus removal relies on ferric chloride or polyaluminum chloride (PAC). These coagulants precipitate the phosphorus, and then a DAF system is used to remove the generated solids.

Placing an Ideal DAF system downstream of an MBBR tank is a compact way to separate biomass and solids from the MBBR process while also creating a low-volume, thick sludge for wasting. Solutions like these easily retrofit into existing tanks to upgrade wastewater treatment operations.

Achieving success

The key to success for pet food manufacturing plants to comply with regulations, meet business targets, reduce treatment costs and minimize their environmental impact is identifying the required wastewater removal methods to meet effluent limits. These factors, in turn, will inform the design of an effective wastewater treatment solution.

Chandler Johnson is chief technology officer at World Water Works, Inc.

World Water Works