Contents
- How to use this guide
- What “slime” really is and why it hurts production
- Where biocides fit in a full deposit-control program
- Key selection factors
- Biocide families and typical roles
- Feed points & strategy (continuous vs slug, rotation)
- Monitoring signals (ATP, dipslides, ORP, visual)
- Compatibility & side effects (wet end, sizing, foaming)
- Troubleshooting: symptoms → likely causes
- Procurement specs & acceptance checks (COA/SDS)
- RFQ notes
- FAQ
How to use this guide
This is a practical decision aid for mill operations, EHS, and procurement teams. Use it to align on program goals (runnability, cleanliness, odor, quality), what you will measure (KPIs and sampling points), and how you will specify supply (COA/SDS, packaging, lead time).
Safety-first: Always follow the supplier SDS/label and site procedures. This guide describes program design principles—not product-specific dosing instructions.
What “slime” really is and why it hurts production
In paper machines, “slime” usually means microbial growth and associated deposits (biofilms + trapped fines, starch, pitch, and fillers) in warm, nutrient-rich white-water loops. The impact is not only microbiological—slime becomes a deposit engine.
Common operational symptoms
- Sheet breaks and unstable wet-end performance
- Felt/roll contamination and drainage loss
- Odor and discoloration, spot defects, holes
- Increased cleaning frequency, downtime, and chemical spend
Why it gets worse in closed water
- Higher temperature and higher dissolved/colloidal organics (COD)
- More nutrients from starch and additives
- Shorter “flush” to sewer; longer residence time
- Biofilm shielding: deposits protect microbes from treatment
Where biocides fit in a full deposit-control program
The most reliable programs treat slime as part of deposit control: reduce nutrients where possible, prevent attachment/biofilm, and apply biocides with sufficient contact time and verification.
| Program layer | What it targets | Examples | Commercial note |
|---|---|---|---|
| Housekeeping & cleaning | Existing deposits and growth sites | Targeted cleaning plans, shower hygiene, chest cleaning | Often highest ROI before adding more biocide |
| Biocide strategy | Planktonic microbes + biofilm pressure | Oxidizing and/or non-oxidizing rotation | Optimize delivered cost per ton at stable runnability |
| Deposit aids | Stickies/pitch and organic deposition | Dispersants, detackifiers, fixatives | Reduces “habitat” for microbes |
| Monitoring & control | Early warning + proof of control | ATP trends, dipslides, ORP/residual (oxidizers), inspections | Prevents reactive over-dosing |
Key selection factors
Biocide selection is not “one product fits all.” The best approach starts with your system conditions and constraints.
System conditions
- Temperature profile and residence time
- pH window and alkalinity
- Organic load (COD), starch level, closure degree
- High-solids zones (saveall, chests) vs low-solids loops
Performance goals
- Reduce sheet breaks and felt/roll deposits
- Improve drainage and formation stability
- Control odor and slime-related defects
- Lower cleaning downtime and off-spec waste
Constraints
- Effluent/discharge limits and toxicity goals
- Material compatibility (stainless, plastics, elastomers)
- Interactions with wet-end chemistry (retention, sizing)
- Storage, handling, and site safety requirements
Biocide families and typical roles
Programs often combine an oxidizing tool (fast knockdown where demand allows) with a non-oxidizer rotation (broad spectrum and biofilm pressure). Actual selection must follow local regulatory approvals and your mill constraints.
| Category | Typical role | Operational notes | What to verify in trials |
|---|---|---|---|
| Oxidizing biocides (e.g., chlorine dioxide, hypochlorite, peroxide/peracids) |
Fast reduction of activity where oxidizer demand is manageable | Performance depends on demand; requires defined sampling points and control signals (often ORP/residual) | Impact on odor, deposits, corrosion risk, and compatibility with additives/color |
| Non-oxidizing biocides (e.g., isothiazolinones, DBNPA, bronopol, glutaraldehyde, quats — where permitted) |
Rotation tool, biofilm pressure reduction, targeted control in high-demand systems | Effectiveness depends on contact time and feed-point; rotation helps manage tolerance and spectrum gaps | Foam tendency, wet-end interactions, felt cleanliness, and stability at your pH/temperature |
Commercial tip: compare suppliers on total program cost (delivered cost + operational impacts), not only product price. Stable runnability and fewer breaks can outweigh small differences in chemical €/kg.
Feed points & strategy (continuous vs slug, rotation)
A biocide can be “good on paper” and still fail if it is added at the wrong point. Program design is about ensuring the treatment reaches the growth zones with enough contact time, then verifying with measurements.
Feed-point principles
- Treat the high-risk zones: warm chests, high organics, low shear dead-legs
- Protect critical surfaces: approach flow, showers, and recirculation loops where deposits trigger breaks
- Define contact time: dose upstream of the zone you want to impact
- Standardize sampling points: “same place, same time” beats random testing
Strategy patterns mills use
- Continuous maintenance (stability) + periodic boosts (pressure reduction)
- Rotation of chemistries to maintain spectrum and reduce tolerance risk
- Cleaning synchronization: treat after cleaning to delay regrowth
- Seasonal adjustments: warmer months often require higher control intensity
Monitoring signals (ATP, dipslides, ORP, visual)
The best programs connect microbiology measurements to operational outcomes. Choose a small KPI set you can execute consistently.
| Signal | What it tells you | Pros | Common pitfalls |
|---|---|---|---|
| ATP trend | Rapid indication of biological activity changes | Fast, sensitive, good for trending | Absolute numbers vary by matrix; focus on consistent sampling and trends |
| Dipslides / plate counts | Culture-based indicator of growth pressure | Simple, inexpensive | Slow results; not all organisms culture well; interpret as trend |
| ORP/residual (oxidizers) | Whether oxidizer is present at the sampling point | Operational control signal | High demand can mask performance; ORP alone does not prove biofilm control |
| Visual/inspection | Deposit location and severity | Highly actionable | Infrequent checks miss early-stage growth; document with photos and locations |
| Process KPIs | Real business impact | Directly tied to value | Lagging indicators; combine with early-warning microbiology |
Minimum KPI set (practical)
Pick 3: ATP trend at defined points, sheet breaks / downtime, and felt/roll deposit scoring. If oxidizers are used, add ORP/residual at a single agreed control point.
Compatibility & side effects (wet end, sizing, foaming)
Paper machines are chemistry-dense. Biocides can interact with wet-end additives or influence deposits indirectly. Validate compatibility in trials and watch for unintended shifts.
| Area | What can go wrong | What to check |
|---|---|---|
| Wet-end performance | Retention/drainage variability, charge balance shifts | Jar tests/trials; monitor zeta/charge demand if used at your site |
| Sizing (ASA/AKD) | Deposit risk changes; emulsion stability impacts | Track sizing efficiency, deposits near dosing points, and emulsion stability indicators |
| Foam | Foam increases, deaeration issues | Foam observation, defoamer demand changes, headbox stability |
| Materials & corrosion | Accelerated corrosion with certain oxidizers or poor control | Confirm metallurgy and elastomer compatibility; verify control strategy and inspection |
| Effluent impacts | Toxicity excursions or permit issues | Align with EHS; request guidance on discharge profile and regulatory status |
Troubleshooting: symptoms → likely causes
| Symptom | Likely causes | First checks |
|---|---|---|
| Slime returns quickly after treatment | Biofilm shielding, wrong feed point, insufficient contact time, inconsistent dosing | Confirm pump calibration and feed location; inspect known growth zones; align cleaning + treatment timing |
| Odor persists | Anaerobic pockets, high organic load, dead-legs | Map low-flow zones; evaluate housekeeping/flush points; verify control signals at the odor source area |
| Sheet breaks increase after “program change” | Deposit release (“sloughing”), compatibility issues, foaming | Review change timing; inspect felts/rolls; monitor foam and wet-end stability; adjust transition plan |
| Oxidizer seems ineffective | High demand consuming oxidizer before target zones | Use defined control point (ORP/residual) and compare demand; consider feed strategy or rotation with non-oxidizer |
Procurement specs & acceptance checks (COA/SDS)
For stable performance, procurement must ensure consistent product identity and quality, and operations must have reliable logistics and documentation.
| Category | What to request | What to verify on receipt |
|---|---|---|
| Identity & traceability | Product name/grade, manufacturer, batch/lot, production date | Label and COA match PO; traceability retained |
| Quality (COA) | Appearance, active content (as applicable), density, pH, viscosity range | COA within agreed limits; no separation; packaging intact |
| Regulatory & EHS | Current SDS; regulatory status for your market; handling/storage requirements | EHS approval complete; storage conditions meet requirements |
| Packaging | Drum/IBC/bulk options, liner/closure type, labeling language | Compatible with your dosing equipment and secondary containment |
| Logistics | Lead time, Incoterms, shelf life, temperature limits, transport classification | Reorder point and safety stock defined; FEFO inventory practiced |
Commercial note: ask suppliers to propose a program package (primary + rotation option + monitoring support) and quote delivered cost with packaging/Incoterms. This reduces hidden cost and response time when issues occur.
RFQ notes (what to include)
- Machine & system: grade, speed, closure level, key chests/loops, known growth zones.
- Water chemistry: pH, temperature range, COD/starch levels, conductivity/hardness if relevant.
- Current symptoms: breaks, odor, deposit locations, downtime frequency, seasonal effects.
- Constraints: discharge limits, material compatibility, any product restrictions/approvals.
- Program goals: reduce breaks, improve felt life, lower cleaning downtime, control odor/defects.
- Volumes: monthly demand estimate, packaging preference (drum/IBC/bulk), destination/incoterms.
- Documentation: SDS/COA, batch traceability, handling/storage guidance.
FAQ
Should we use one biocide or a rotation?
Many mills use a rotation to broaden spectrum and reduce tolerance risk, especially in closed water and high organic load. The optimal approach depends on your system conditions, constraints, and how consistently you can execute the program.
What’s the fastest “first improvement” step?
Standardize sampling points and trend one microbiology metric (ATP or dipslides) alongside runnability metrics. You’ll quickly see whether changes are real and where the program is not reaching.
Can we treat slime without addressing deposits and cleaning?
Usually not reliably. Biofilm and deposit matrices protect microbes and create regrowth sites. The most stable programs combine targeted cleaning/housekeeping with a verified biocide strategy.
Educational content only. Always follow site EHS rules and the supplier SDS/label for safe use. Program effectiveness depends on system conditions, feed points, and verification. Share your system map and constraints for a tailored shortlist.