ETP for Paper and Pulp Mills
Large-volume primary clarification, biological treatment, and AOX/colour management for paper and pulp mill effluent — handling lignin, fibres, and bleaching chemicals while meeting CPCB-notified effluent standards
Industry Overview
ETP for Paper and Pulp Mills
The paper and pulp industry generates some of the highest-volume industrial wastewater in India, with integrated kraft pulp and paper mills producing 50–200 m³ of effluent per tonne of paper produced. India's paper and pulp sector — with mills in Andhra Pradesh (ITC Paperboards), West Bengal (Hindustan Paper), Maharashtra (Ballarpur Industries), and Kerala — faces specific CPCB-notified effluent standards (separate from General Standards) targeting colour, adsorbable organic halogens (AOX), and BOD. CPCB classifies large integrated pulp and paper mills as Red category with OCEMS requirements, while small and medium paper mills using recycled fibre (non-wood fibre, waste paper) are classified as Orange or Green category depending on capacity.
Paper and pulp mill wastewater is characterised by high colour (from lignin and tannins in pulping liquor), very high suspended solids (paper fibres, fines, coating materials), moderate-to-high BOD and COD, and AOX from chlorine-based bleaching operations. Colour-imparting compounds — primarily lignin and its oxidation products from the pulping and bleaching stages — are partially refractory to conventional biological treatment. The bleaching sequence in kraft mills historically used chlorine-based chemicals generating chlorinated organic compounds (AOX), which are persistent, bioaccumulative, and regulated under CPCB's pulp and paper effluent standards. Modern mills have largely switched to Elemental Chlorine Free (ECF) or Total Chlorine Free (TCF) bleaching, significantly reducing AOX generation.
Spans Envirotech designs ETP systems for medium and large paper and pulp mills, recycled fibre mills, and board mills. Our approach includes primary clarification for high-SS removal, MBBR biological treatment for BOD polishing, coagulation for colour and residual COD reduction, and AOX management through process integration (ECF/TCF bleaching support). Treated ETP effluent from properly designed systems is suitable for partial reuse in non-critical paper making processes, reducing freshwater intake. See our MBBR technology page and our DAF technology page for process details.
Industry Challenges
Key Environmental Challenges
High Suspended Solids from Fibres and Fines
Paper and board mill wastewater contains 1,000–5,000 mg/L of paper fibres, coating pigments, and fine particles. These must be removed before biological treatment — both to protect the biological system and to recover the paper fibre for reuse or as a by-product. Primary clarification (settling with polymer dosing) or dissolved air flotation for finer particles is required as the first treatment step.
Lignin-Based Colour and COD
Pulping liquor (kraft black liquor, sulphite liquor) contains lignin degradation products that impart intense dark colour and contribute to COD. While lignin itself is largely non-biodegradable, the lower-molecular-weight fragments are partially biodegradable. Biological treatment reduces COD by 40–65% but leaves residual colour that requires coagulation-flocculation for further reduction. CPCB pulp and paper standards include colour limits expressed as ADMI or dilution factor.
AOX from Chlorine Bleaching
Chlorine-based bleaching (Cl₂, ClO₂, or hypochlorite) reacts with lignin to form chlorinated organic compounds — measured as Adsorbable Organic Halogens (AOX). CPCB's pulp and paper notification specifies AOX limits of ≤0.8 kg/tonne of paper for new mills. AOX is difficult to remove from wastewater once formed — the primary management strategy is process substitution (ECF or TCF bleaching) rather than ETP treatment. Activated carbon adsorption can reduce trace AOX in ETP effluent.
Large Volume and ETP Scale
An integrated kraft mill producing 200 tonnes per day of paper generates 10,000–40,000 m³/day of effluent — requiring large-scale ETP infrastructure with primary clarifiers of 30–80 m diameter, large MBBR reactors (>10,000 m³), and significant land area. Capital cost for large mill ETP runs ₹25–80 crore. Operating cost optimisation (aeration energy, sludge management) has significant impact on unit production cost.
Sludge Volume and Management
Primary clarifier sludge (paper fibre sludge) and secondary biological sludge together can reach 30–80 kg dry weight per tonne of paper produced. Primary fibre sludge can often be returned to the paper machine as filler (if clean) or converted to briquettes. Secondary biological sludge requires dewatering and is disposed as a non-hazardous solid waste. The combined sludge management system — thickeners, belt filter press or centrifuge, sludge storage — is a significant ETP component.
Our Solutions
Tailored Wastewater Treatment Solutions
Primary Clarification for Fibre Recovery
Large-diameter primary settling tanks (30–60 m diameter) with polymer dosing for efficient fibre and fines removal. Settled fibre sludge (white water recovery) assessed for reuse on paper machine or dewatered and sold as filler/pulp supplement.
MBBR Biological Treatment
Large-scale MBBR for BOD and partial COD reduction from paper mill effluent. Organic surface loading rates of 3–6 g COD/m²·day on high-density carrier media. MBBR preferred over activated sludge for large mills due to lower sludge production per kg BOD removed and easier management.
Coagulation-Flocculation for Colour Removal
Alum or PAC dosing followed by polymer and flocculation for colour reduction (ADMI reduction of 60–80%) and residual COD polishing after biological treatment. Effective for lignin-based colour compounds.
ECF/TCF Bleaching Support for AOX Reduction
Process engineering support for transition from Cl₂-based bleaching to Elemental Chlorine Free (ECF, using ClO₂ only) or Total Chlorine Free (TCF, using O₂, O₃, H₂O₂) bleaching sequences. This is the most effective AOX management strategy — addressing AOX at source rather than in ETP.
Treated Water Internal Recycling
Post-biological treated effluent with colour reduced by coagulation can be recycled for non-critical paper machine uses: shower water, dilution water, wire and press shower, reducing freshwater intake by 30–50%.
Technologies
Proven Technologies for Your Industry
Benefits
Why Choose Spans for Your Industry
- Primary fibre sludge recovered and returned to paper machine or sold — reducing solid waste
- BOD <30 mg/L and COD <250 mg/L compliance under CPCB Paper Mills notification
- Colour management through coagulation achieves dilution factor compliance
- AOX reduction through process bleaching change supported by our engineering team
- 30–50% treated water recycling reduces freshwater intake and discharge volume
- MBBR biological treatment appropriate for large-scale paper mill ETP
Success Stories
Case Studies
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