In an exclusive interaction with Paper Mart, Mr. Pawan Agarwal, Managing Director, Naini Papers Limited, highlighted that the benchmark for water consumption in an integrated agro-based mill has significantly reduced from around 60 m³/tonne to nearly 26–29 m³/tonne. He noted that pushing freshwater reduction beyond this threshold may compromise product aesthetics, elevate corrosion risks, and disrupt thermal balance within the process. However, looking ahead, emerging technologies such as advanced oxidation processes, digital twin modelling, and advancements in tertiary treatment can further optimize freshwater usage while maintaining operational efficiency and paper quality.
Managing Director, Naini Papers Limited
Paper Mart: After implementing water reuse, recycling, and closed-loop systems across your mill, what is your current specific freshwater consumption (m³/tonne), and has this figure stabilized in recent years?
Pawan Agarwal: Specific freshwater consumption is the ratio of total freshwater intake to the total saleable paper produced. For an integrated agro-based mill, the benchmark has shifted from 60 m3/tonne to approximately 26 – 29 m3/tonne.
Stability indicates that the mill has reached a “Closed-Loop Equilibrium.” When this figure stabilizes, it means the internal recycling loops (backwater recovery) are balanced against the inevitable losses from evaporation in the dryer section and moisture in the sludge/final product.
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PM: Under your present operating regime, where water reuse and recycling systems are already in place, what operational challenges have emerged in terms of process stability, machine performance, or water quality?
PA: One of the operational challenges that have emerged in terms of process stability, machine performance, or water quality is wet-end chemistry. As water is reused, “anionic trash” (dissolved organic/inorganic impurities) builds up, interfering with retention aids and strength additives.
Microbial growth is another challenge that arises where warm, nutrient-rich recycled water is a breeding ground for bacteria. This leads to “Slime” formation, causing paper breaks and “holes” in the sheet.
Further, system conductivity is an additional challenge where higher recycling increases the ionic concentration and can suppress the “swelling” of fibers, leading to reduced bonding strength and lower paper quality.
PM: At your current level of system closure and reuse, what process, raw material, or product quality requirements limit further reduction in freshwater consumption?
PA: We limit further reduction in freshwater consumption due to product aesthetics, corrosion risk and thermal balance. For Writing & Printing (W&P) grades, high recycling can cause brightness reversion (yellowing) due to the concentration of residual lignin and chemicals in the backwater. Further, the concentration of chlorides reaches a threshold where even stainless steel faces ‘‘Pitting Corrosion,’’ risking catastrophic equipment failure. Lastly, water acts as a heat sink. Excessive closure can lead to “overheating” of the process water, which negatively affects vacuum pump efficiency and drainage on the wire.
PM: In highly recycled operating conditions such as yours, do you periodically purge water from the system? What operational factors make this necessary, and how does it define your minimum freshwater intake?
PA: The Purge Principle: A “purge” is a controlled discharge of contaminated water to prevent the buildup of Non-Process Elements (NPEs) like potassium and silica, which are prevalent in agro-residues (straw/bagasse). The minimum intake is mathematically defined by the evaporative demand of the drying cylinders and the cooling towers, plus the water required to keep the Total Dissolved Solids (TDS) below the saturation/scaling point.
PM: With closed-loop and reuse systems already implemented, how do you determine where freshwater must still be used versus where recycled water can be used within different sections of the mill?
PA: We reserve freshwater usage for “critical path” areas where purity is non-negotiable such as high-pressure showers to prevent nozzle clogging and felt damage; chemical/additive dilution to ensure the efficacy of expensive dyes and sizing agents; and gland cooling to protect mechanical seals from abrasive particles. For pulp dilution and brown stock washing, we use recycled water where the organic load is less critical to the final surface finish.
PM: Under these highly recycled conditions, what water quality or system parameters do you monitor most closely, and how do they influence decisions related to reuse levels, purging, or freshwater intake?
PA: The closely monitored parameters for checking water quality are conductivity/TDS, Total Suspended Solids (TSS), and calcium hardness.
Conductivity is the primary proxy for chemical buildup. High conductivity signals the need for a purge. Total Suspended Solids (TSS) monitors the efficiency of our fiber recovery units (Krofta/DAF) and calcium hardness is crucial for preventing scale formation in the heat exchangers and the vacuum system.
PM: After implementing available water reuse and recycling measures, have you reached a practical limit to further water reduction under your current operating configuration? What technical or operational factors define this limit?
PA: The practical limit or the plateau is defined by ‘Solubility Limit’ and the ‘Law of Diminishing Returns’.
Solubility Limit: This is the point where the water is “saturated.” Beyond this, dissolved solids will physically precipitate out, causing massive scaling in piping and machinery.
The Law of Diminishing Returns: The capital expenditure (CAPEX) required to save the “last few drops” (via Membrane Technology (RO) or MVR) often outweighs the environmental and economic benefits.
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PM: Beyond your existing systems and processes, what types of improvements or future technological shifts would be necessary to reduce water consumption further?
PA: Some of the future technological shifts that would be necessary to further reduce water consumption are:
Advanced Oxidation Processes (AOP): Using Ozone (O3) or UV to break down recalcitrant organic matter within the internal loops.
Digital Twin Modelling: Using AI to predict the “system load” and automatically adjust chemical dosing in real-time to compensate for water quality fluctuations.
Tertiary Treatment Evolution: Investing in advanced oxidation processes (AOPs) to break down recalcitrant COD in the recycled loops.
