Dewatering Sludge at a Recycled Paperboard Mill

1. Customer Background & Challenge

Our client is a paper mill in the United States that produces recycled paperboard. They operate a closed-loop water circulation system, which means that impurities and solids continuously build up in the process water with no way to discharge them. Over time, this accumulation affects production quality and efficiency.
They analysed their sludge and found it contained sticky contaminants from the recycled fibres. Their primary goal was to dewater this sludge so they could transport it off‑site for disposal, thereby purging impurities from their system and maintaining cleaner process water.

2. Initial Data & Our Recommended Solutions

The customer provided the following baseline data:

• Flow rate: 1,800 gallons per hour (43,200 GPD)
• Feed solids content: 0.7%
• Target solids after dewatering: ~20% (they didn't need it bone‑dry, just enough to reduce free water for easy handling)
• Material: Sludge with minor adhesive components
• Equipment material: Stainless steel 304

Based on these numbers, we calculated that the dry solids load was about 50 kg per hour. To handle the full 1,800 GPH at 0.7% solids, we recommended a Model 351 Sludge Dewatering Press. However, we also needed to understand the source of the wastewater to confirm the suitability – the client confirmed it was from their paperboard process.
We presented two options:

• Option 1 – Integrated system (Model 351 all‑in‑one): The sludge dewatering press, polymer dosing unit, feed pumps, sludge transfer pumps, piping, and valves were all pre‑assembled on a single skid. The client would only need to connect power and water on site – very convenient and quick to start.
• Option 2 – Single sludge dewatering press (Model 351 only): The client would purchase and install the auxiliary equipment locally (or we could supply them separately). This would save a small portion of the budget but required on‑site piping and installation work.

3. Client's Revised Plan – Partial Capacity

After reviewing their operation, the client estimated that once they started removing solids with the sludge dewatering press, the contaminant level in the circulating water would drop significantly. Therefore, they initially asked for a quotation based on only 50% of the current flow – i.e., 900 gallons per hour. For that reduced flow, we suggested the smaller Model 251 integrated unit, which would be more cost‑effective.
However, they also wanted to test whether their existing flocculant could work with the sludge dewatering press feed conditions. They conducted a trial using their current liquid polymer, which they diluted with fresh water to 1.5%–2.5% concentration using a mechanical pump to activate the polymer chains.
Unfortunately, the test results were not satisfactory – the flocculation was weak, and the sludge did not form stable clumps for effective dewatering.

4. Our Technical Advice & Adjustments

We gave the customer two key pieces of advice:

• For liquid polymer dosing: Instead of pre‑diluting manually, they could use a metering pump to inject the liquid polymer directly into the mixing tank of the sludge dewatering press, where it would mix with the incoming sludge in the right proportion. This is simpler and more consistent.
• Polymer selection: We recommended that they experiment with different types of flocculants available locally to find the one that works best with their specific sludge composition. Since every sludge is different, a proper jar test or on‑site trial would be the most reliable way to optimise performance.

After further testing with various polymers, the customer finally found a suitable flocculant that met the feed requirements of the screw press. At that point, they decided to go with the Model 251 sludge dewatering press only, as they don't need a dosing unit.

5. Final Result – Equipment Shipped

We manufactured the Model 251 sludge dewatering press in stainless steel 304 as per the order. The unit was completed on schedule and is now on its way to the client's site. The customer is looking forward to putting it into operation, which will allow them to continuously remove solids from their closed‑loop system, reduce adhesive build‑up, and produce a dewatered cake with around 20% solids – easy to handle and transport for off‑site disposal.

Here is the video:

Got a tough sludge? Reach out – we love puzzles like this!
📢 Any requirements? Contact us now!