Chip and log washers don’t need rivers of fresh water. Screen the bark and grit, clarify the fines, and mills can recycle 95%+ of woodyard flows — cutting make‑up water to roughly 400 L per tonne of chips.
The pulp and paper business is one of the world’s biggest water users — about 91×10^6 m³ every day — with the Asia‑Pacific region accounting for nearly half (ResourceWise). Yet the industry’s long arc is bending toward closure. Historical fiberlines drew 150–200 m³ of fresh water per tonne of pulp; modern setups run well under 20 m³/ton (air‑dry pulp equivalent) thanks to counter‑current and twin‑roll press washers (Valmet).
In practice, more than 80% of process water is reused internally; UPM Pulp says it returns about 80% of intake water to the environment after treatment (implying only ~20% net consumptive loss) (UPM). The woodyard — where logs and chips are washed to shed dirt, bark, and fines — is now a prime target for deeper cuts.
Woodyard washwater baseline and potential
Washwater from log drums and chip washers carries suspended solids (TSS: total suspended solids) such as bark, sand, and wood fines, often exceeding 1,000 mg/L in raw form. Crucially, chip washing water can be almost completely recycled: a U.S. EPA technical review reports that a closed‑circuit chip washer needs only about 400 L of fresh water per tonne of chips (≈95 gallons/ton) for make‑up, with the balance recirculated (EPA).
Older open systems consumed vastly more — tens of cubic meters per ton. One patent example cites ~19 m³/ton in an unconserved chip wash (an extreme case) (patent). The savings on offer from recycling are therefore on the order of 98–99% (derived from the ~0.4 m³/t closed‑loop make‑up versus tens of m³/t in open mode).
Policy targets and local practice
In Indonesia, APP/Indah Kiat Pulp & Paper is targeting a 30% reduction in water intensity by 2030; the mill reports reusing wastewater from log washers in the log wash process itself, and recycling treated domestic effluent and reverse‑osmosis reject streams for process use (EGINDO) (EGINDO). These moves align with Indonesia’s PROPER “Green” rating framework (noted by the same source).
Rainwater and river catchment also play a role: building a lagoon to capture river water and rain for dry‑season supply is cited as a way to lower make‑up needs; using ambient water also dilutes solids less than relying on fully treated water (EGINDO).
Source‑side measures in the woodyard
Five levers dominate: closed‑loop washing; mechanical screening; minimized spray use; storm/rainwater harvesting; and leak/flow audits. Counter‑current washing mirrors the bleach‑plant logic — the cleanest water contacts the cleanest chips — and enables near‑closure (EPA). Up‑front mechanical cleaning limits solids loading: trommels and screens intercept sticks, bark bundles, and grit before the water circuit (China Pulp & Paper).
Minimizing continuous sprays, switching to on‑demand or high‑impact nozzles, and using dry dust control keep volumes in check. Regular water balances and leak inspections prevent high‑pressure wash lines from bleeding hundreds of cubic meters per day. UPM reports that best‑available techniques (BAT) and closed‑loop systems cut wastewater volume by 30% over 20 years, while reducing effluent COD (chemical oxygen demand) by more than half per ton (UPM).
For primary separation in the woodyard, continuous debris removal via an automatic screen reduces solids loads upstream of the wash loop.
Screening and clarification train
Industry references are consistent: effluents laden with fibers and fines respond well to physical clarification — screening, sedimentation, and flotation (China Pulp & Paper). A two‑step approach dominates.
First, coarse screening (e.g., 10–30 mm apertures) pulls out sticks and bark clumps. A trommel sized for 50–100 m³/h is typically a few meters in diameter and 10–15 m long. Coarse screens alone can skim off >70–80% of TSS by geometry (China Pulp & Paper).
Second, clarification removes the fines: a conventional clarifier or, preferably, a lamella (inclined‑plate) clarifier achieves fast settling in a compact footprint; properly sized units with 2–4 hours of residence remove >90% of remaining solids, and are widely used for high‑fiber effluents (China Pulp & Paper). A chemical assist — small coagulant or polymer dosing — agglomerates fines when needed. Where dosing is applied, mills often meter coagulant with a dosing pump and tailor polymers from flocculant programs.
For polishing, some sites add dissolved‑air flotation (DAF), where bubbles attach to fine fibers and float them for skimming — a role filled by a compact DAF unit. For most woodyards, screening plus settling is sufficient, and the clarified effluent — often comprising >90% of the flow — is pumped back to the washers. Bench tests indicate that re‑used washwater does not adversely affect chip quality or downstream pulping, provided solids are removed (EPA).
Lamella installations typically use a lamella settler to compress surface area into a small footprint.
Closed‑loop system design parameters
A typical loop integrates these elements (Figure 1 conceptual): a surge/equalization tank for flow buffering and grit drop‑out; coarse screening; optional fine screening; clarification; recycle pumping; make‑up water; and sludge handling. Equalization smooths peaks and protects downstream units.
Coarse screens are often stainless steel wedge‑wire; rejects head to a bark conveyor for use as fuel or disposal. A second screen (2–5 mm) or a rotary drum (cloth) filter can follow where very fine bark or sand is a problem. Clarification then does the heavy lifting: sizing rules of thumb for lamella units assume an overflow rate of ~1–2 m³/m²·h treating pulp washwater. A 500 m³/h flow therefore calls for roughly 250 m² of plate area at 2 m/h flux. Depth should provide 1–4 hours detention; rakes or gliding scrapers collect underflow sludge at ~3–5% solids.
Make‑up is small: the EPA’s closed‑circuit figure of ~400 L/ton chip implies ~400 m³/day of fresh water for a 1,000 tpd chip line (EPA). Many mills source this from treated rainwater or municipal supplies. Sludges (bark fines, wood fiber) are dewatered (e.g., belt or screw press) or routed to general sludge handling; some facilities combust dried solids for energy.
Where post‑clarifier cleanup is needed, a final sand bed offers low‑cost polishing; a simple sand/silica media filter can meet typical woodyard clarity targets.
Measured outcomes and economics
Consider a woodyard washing 2,000 tonnes/day. In open mode, fresh draw might be ~0.4–0.8 m³/t (modern values); in closed‑loop it can fall to ~0.4 m³/t or less (EPA). That’s ≈800 m³/day of make‑up. If the open system used ~4,000 m³/day, closing the loop saves ~3,200 m³/day — an 80% reduction. At Indonesian industrial tariffs of roughly $0.50–1 per m³, plus sewer charges, the water bill drops by about $1–2 million per year.
Performance data are consistent across literature: screening and clarification can remove 85–95% of suspended solids, producing clarified water under ~200 mg/L TSS (China Pulp & Paper) (China Pulp & Paper). Fresh make‑up typically falls by ~80–95% versus open systems (EPA), and effluent flow drops proportionally, lowering downstream BOD/COD loads (biochemical/chemical oxygen demand).
At the mill scale, closing woodyard washers helps push overall water use down — e.g., from ~50 m³/ton to ~5–10 m³/ton on a sample site. For context, classic Kraft pulp permits in Indonesia cite ~65 m³/ton for standalone pulp and ~45 m³/ton for integrated paper, whereas older mills without recycling topped 100+ m³/ton (Studylibid).
Membrane add‑ons for deeper reuse
While mechanical trains already enable high reuse, newer membrane options are pushing toward near‑zero external discharge in pulp circuits (Water Online) (Valmet). One Dutch consortium reported 95% recovery using direct nanofiltration; in comparable roles, mills evaluate nano‑filtration for moderate‑pressure separations and ultrafiltration as pretreatment or fiber barriers. In biological circuits, membrane bioreactors (MBR: biological treatment coupled to membranes) are deployed to produce reuse‑quality water — an approach reflected in packaged membrane bioreactor systems.
Case references and design cautions
Valmet credits counter‑current closures with cutting fiberline water use by ~90% over past decades (Valmet). EPA studies confirm chip‑washing losses are minimal in recycled operation (EPA). A Dutch demo plant highlights 95% reuse with direct nanofiltration (Water Online). Indonesian mill disclosures underscore internal recirculation and reuse to meet “Green” performance ratings (EGINDO) (EGINDO).
Design is plant‑specific: screen sizes, clarifier volumes, and residence times must match solids profiles. A conventional sedimentation clarifier remains viable where footprint allows; inclined plates deliver the same physics in a smaller package via a lamella settler. Figure 1 (Conceptual): log/chip washers → surge tank → screens → clarifier → recycle pump, with only make‑up and sludge discharge.
Bottom line
The woodyard can move from “open drain” to “closed loop” with proven unit ops: coarse screening to stop big debris, clarification to settle fines, and optional flotation or sand polishing. The result, repeatedly documented, is >90% water recovery, ~80–95% cuts in make‑up versus open systems, and lower effluent loads — translating to multi‑million‑dollar annual savings as water and discharge tariffs rise (China Pulp & Paper) (China Pulp & Paper) (EPA) (Valmet).
