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Selecting the Right Dissolved Air Flotation for your Application

Andrew Marsh

Many industries have some level of wastewater pretreatment before discharging to the local Publicly Owned Treatment Works (POTW). In the food and beverage industry, pretreatment with Dissolved Air Flotation (DAF) is common to remove fats, oils and greases, along with associated Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS). These food and beverage companies are in the business of making their products, not wastewater treatment. So, often times, selecting the right piece of equipment can be a challenge.

Dissolved Air Flotation Equipment

DAF Rendering for illustration purposes only.

There are more than 17 different manufacturers of DAF equipment. Each is trying to sell their piece of equipment and each sincerely believes they have the right choice for you. So how do you decide? Choosing the right manufacturer and the right piece of equipment is essential to meeting the needs of your company to comply with its industrial pretreatment agreement or direct discharge (NPDES) permit.

Some DAF manufacturers may focus on a particular industry, such as the pulp and paper industry while others will focus on the meat processing industry. Not all DAFs may be right for your application. Consider the market focus of the DAF manufacturer.

Critical Factors & Navigating Guide

There are a myriad of DAF manufacturers and many, if not all, claim they have an excellent piece of equipment that will do the job – for almost any application. So, what are the most important considerations and key design criteria when selecting a new DAF for your facility?

  • Track Record: One of the most important factors in selecting a new DAF is the track record of the manufacturer.
  1. How long has the firm been in business?
  2. How many installations does the manufacturer have under its belt?
  3. How many of those installations are similar to your application?
  4. How satisfied are the manufacturer’s references/installations?Not all manufacturers can be expected to have a long list of nearby, similar and successful installations. In fact, some manufacturers may have few if any installations in your industry, in your geography and/or in the size/capacity that is needed. No one wants to be the first person to try a new piece of wastewater treatment equipment. Wastewater treatment requires extremely reliable equipment that typically runs night and day, every day, every week, every year.
  • Capacity: Often times, a food and beverage company will build a facility that includes a production line and a wastewater pretreatment facility of some kind. Over time, the company and the facility grow and production lines are added. Unfortunately, the capacity of the pretreatment equipment is sometimes overlooked during production expansions and wastewater equipment can be overwhelmed. This can lead to permit violations and expensive fines, legal impacts and bad public relations.Evaluating the design capacity – both for hydraulic capacity and loading (such as BOD and COD) is necessary for each production expansion to ensure compliance with industrial pretreatment agreements with local and state regulators.

    Not all DAF manufacturers make the range of capacity that may be the right fit for your application. It is important to consider the available product line from the DAF manufacturer and make sure they have a successful working history with the size DAF that is right for you. Whether the DAF you choose is a custom size or a standard model, we recommend staying within the range of most of the other sizes made by that manufacturer.

    Goldilocks wanted the chair that was just right, not too big or too small. The same can be said of the right size DAF for your application. If the unit is undersized, the equipment will be overwhelmed and can lead to permit violations, etc. If the unit is too large, or oversized for your application, the capital cost may be too high for your needs. The right size DAF for your application will be just right to handle the flow and loading and not break the bank.

  • Footprint: Fitting a new DAF into an existing facility can be a challenge. Consider the dimensions of the unit you need (round or rectangular), the ancillary equipment including controls and how it will fit in the space available. Using plate settlers in the DAF can reduce the footprint of the DAF but not all Owners like the maintenance associated with plate settlers. Circular DAFs may not be a good use of space for a tight footprint as well. Critical design parameters such as solids loading rate and hydraulic loading rate are related to footprint. In the absence of side-by-side pilot testing, a comparison of critical design parameters is the best indicator of performance. The air to solids ratio is another key design parameter that should be included in any evaluation.
  • Constructability: More than likely the production line will need to stay in service and therefore, the existing wastewater treatment will need to stay in service while the new equipment is installed, started up and commissioned.Consider where the new equipment can reside while the old equipment is operating and how to repurpose the old equipment space when it can be decommissioned.
  • Materials of Construction: The application and the environment in which the DAF equipment is located can have a pronounced impact on the life of the equipment. DAF equipment comes in a variety of materials from carbon steel to stainless steel to plastic. Often, wastewater pretreatment areas of a plant are very high temperature, very wet, high humidity environments. Often times the considerations for corrosion can lead to selecting a more corrosion resistant material.
  • Service: Consider where your closest service person is geographically based.
  1. Where will your service technician be travelling from?
  2. How responsive are they?
  3. What is the cost of a service call?

Usually, when service is needed for a food and beverage company’s wastewater treatment equipment, the facility wants to stay in production and it’s very costly to stop production to wait while a piece of equipment is repaired. You may find the geography of the DAF manufacturer and the service call cost can be an important factor in selecting the right DAF for your application.

  • Warranty: Consider the warranty on the equipment and what the warranty covers. Often times a manufacturer’s warranty only covers the parts that need to be replaced. The true cost of a breakdown can be tremendous including not only parts but also labor, production downtime, etc. Consider the warranty duration and what is covered when selecting the equipment.
  • Operation and Maintenance: A TWO-WAY street. Consideration should be made to select DAF equipment that is easy to operate and maintain and in general is very reliable and requires very little maintenance. Having said that, it’s not all on the manufacturer to make the greatest product in the world. All equipment, no matter how well engineered and manufactured, requires some level of care for proper operation and maintenance. Most food and beverage industries have very well defined roles and responsibilities including performance metrics and key performance indicators (KPIs) for their employees who make their products. Can the same be said for the employee(s) tasked with oversight of the operation and maintenance of the wastewater treatment equipment?
  1. Are the employees responsible for wastewater treatment assigned metrics based on routinely meeting the facility’s industrial pretreatment permit requirements and minimizing downtime?
  2. Is the routine preventative maintenance assigned to an employee that will make sure it gets done regularly and done right?
  3. Have these employees been properly trained on the equipment and given the tools necessary to do their job?
  4. Are maintenance windows realistically scheduled, perhaps during production outages, sometimes over holidays, when other production maintenance may be more critical?

All these are important considerations when selecting a DAF.

Some may be wondering why capital cost has not been mentioned. Why is this not the first and most important criteria? There is an important reason why cost is not mentioned first. Once all these other critical factors are considered and the right DAF manufacturer has been found, the consumer will discover the right DAF with the best value, not necessarily the least cost, has been found. A few dollars more spent up front on the capital cost could save you many headaches down the road, especially if you are paying for routine service calls from far away and your DAF manufacturer is not responsive, for example.

HR Green can help you navigate the waters of wastewater treatment equipment selection to meet your industrial pretreatment permit needs. If you would like to learn more contact Andrew Marsh at amarsh@hrgreen.com

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