Start with the factory’s wastewater, not the DAF catalogue
No single ETP or DAF configuration can be prescribed for a factory in Medan, Indonesia, from location alone. A factory generally needs DAF when wastewater contains oil, grease, FOG, fine suspended solids, colloids or other buoyant contaminants that screening cannot remove. DAF attaches microscopic bubbles to contaminants so the float can be skimmed, but it does not replace biological treatment for biodegradable dissolved load. A complete industrial effluent treatment plant may also require equalization, screening, chemical dosing, biological treatment, polishing, disinfection and industrial sludge dewatering. Final selection depends on measured flow, wastewater characteristics, reuse or discharge objectives, site constraints and confirmed local requirements.
Begin with representative samples covering production, cleaning and shutdown periods. For each stream, record average and peak flow, shift pattern, pH, temperature, oil and grease, TSS, COD and BOD, and identify the process causing the load. A single midday sample can conceal the cleaning discharges or batch dumps that determine the required equalization and treatment capacity.
Separate concentrated streams at source where practical. Diluting a high-strength stream in a large equalization tank can make the mixture appear manageable while making reliable sizing harder, increasing chemical demand and residual load on biological treatment.
Screening protects downstream equipment from rags, plastics and fibrous debris; it is not an oil, grease, colloid or dissolved-load treatment process. An inclined mechanical bar screen may form part of pretreatment, but its selection should follow the material and debris actually present.
Next, establish whether the treated water will be discharged, enter a sewer, be reused in a process or serve another approved purpose. That decision changes the required treatment, monitoring and documentation. The supplied research contains no verified Medan-specific effluent limits. The responsible Indonesian authority and receiving utility must confirm the current criteria before final design.
Use contaminant and flow triggers to select the treatment route
DAF is the core physical-chemical stage when oil, grease, FOG, fine solids or colloids are significant. PT Hydromart’s Indonesian DAF overview, published in 2026, identifies DAF as widely used for oil refineries, petrochemical and chemical plants, natural-gas processing plants and paper mills. It removes suspended matter by releasing microscopic bubbles at atmospheric pressure, attaching them to buoyant contaminants and skimming the resulting float.
The next decision depends on where the contamination occurs in the process train. DAF can serve as primary clarification before biological treatment or as polishing after biological treatment. A fat- and oil-rich stream can justify upstream DAF, while a DAF placed after biological treatment can capture residual floatable material. A dissolved biodegradable load that remains after physical separation calls for biological treatment; filtration, disinfection or advanced treatment should be added only when the receiving-water criteria, reuse target or process-water specification requires them.
Coagulation and flocculation should precede DAF when emulsified oils, colloids or fine particles must be captured. Spans Envirotech’s DAF design guide, published in 2026, states that DAF performance for colloidal and emulsified contaminants can be poor without chemical preparation. Use jar testing to establish the coagulant, flocculant, pH and mixing sequence before fixing the dosing system.
| Measured condition | Treatment implication | Information still required |
|---|---|---|
| Oil, grease or FOG is significant | Evaluate DAF with source control and chemical preparation | Oil and grease concentrations, emulsification, flow variability and removal target |
| Fine TSS or colloids dominate | Evaluate coagulation, flocculation and DAF | TSS, particle distribution, pH, chemical demand and jar-test results |
| Biodegradable organics remain after physical separation | Add biological treatment | COD, BOD, temperature, biodegradability and shock-load conditions |
| Water will be reused | Define the required polishing route | Reuse specification, process sensitivity and monitoring requirements |
Include sludge handling from the beginning. Spans reports that DAF float typically contains 2–6% total solids and may require filter-press or belt-press dewatering. Peak flow, wastewater variability, chemical demand, footprint, operator competence and the final discharge or reuse objective remain project-specific inputs; none can be inferred from the factory location alone.
Size the DAF unit around hydraulic loading and operating conditions
A DAF quotation should state the design flow and hydraulic surface-loading rate, not just tank dimensions. Spans identifies 3–6 m³/m²·hr as the standard industrial benchmark, while high-rate systems using lamella plates or tube settlers may reach 10–15 m³/m²·hr. It also identifies 4 m³/m²·hr as a common conservative design point for dairy and food wastewater. That value is not transferable to every Medan factory without wastewater testing.
The same guide gives a useful sizing relationship: a DAF treating 100 m³/hr at 3–6 m³/m²·hr requires 17–33 m² of flotation-tank plan area. Confirm whether the quoted area is the effective flotation area, total tank area or the footprint after adding contact, separation and sludge-collection zones. DAF system engineering specifications provide a useful basis for checking that distinction.
Operating parameters must be linked to the contaminants. Spans reports saturation pressure of 4–6 bar gauge and an air-to-solids ratio of 0.005–0.060 mL air/mg solids, equivalent to 5–60 mL/g. These are design references rather than automatic settings; recycle and air demand should follow the selected hydraulic and contaminant loading.
Typical industrial recycle is 15–50%. Spans identifies 25–35% as common for dairy and food applications and states that 40–50% may be required when TSS exceeds 500 mg/L. The contact zone should provide 1–3 minutes of retention with gentle mixing, because turbulent inlet mixing can break flocs and reduce removal efficiency.
| Design field | Supported reference | Procurement check |
|---|---|---|
| Hydraulic surface loading | 3–6 m³/m²·hr standard; 10–15 m³/m²·hr for high-rate configurations, according to Spans 2026 | State selected rate, effective area and peak-flow basis |
| Saturation pressure | 4–6 bar gauge, according to Spans 2026 | Identify compressor, pressure control and receiver scope |
| Air-to-solids ratio | 0.005–0.060 mL air/mg solids, or 5–60 mL/g, according to Spans 2026 | Base the guarantee on measured solids loading |
| Recycle ratio | 15–50% typical; 25–35% common for food and dairy; 40–50% may be needed above 500 mg/L TSS, according to Spans 2026 | Confirm flow, pressure, air demand and energy consumption |
| Contact-zone retention | 1–3 minutes with gentle mixing, according to Spans 2026 | Exclude high-energy inlet mixing from the guaranteed design |
Compare the required flow and space envelope against the offered DAF configuration. The supplier’s published model range is a commercial catalogue input, not evidence that one model fits the factory’s wastewater or site.
Build the complete wastewater treatment process
A workable process train may run from source segregation through equalization, mechanical screening, pH adjustment, coagulation and flocculation, DAF, biological treatment where required, filtration or polishing, disinfection where required, and controlled sludge dewatering. Each stage should have a stated purpose, design flow, monitored parameter, bypass condition and owner. This structure is more useful than a list of equipment because it exposes missing treatment steps before procurement.
Chemical inputs must be established through testing. Spans lists example doses of alum at 50–200 mg/L, ferric chloride at 30–100 mg/L, PAC at 10–50 mg/L and polyacrylamide at 0.5–3 mg/L. These are not automatic doses for a Medan plant. For emulsified oil in food and dairy wastewater, the same 2026 guide identifies pH adjustment to 4.5–5.5 as a way to improve separation by breaking oil-in-water emulsions; jar testing should establish the actual operating pH and dose.
Use a PLC-controlled chemical dosing system where continuous feed and operator consistency are required. Verify compatibility with the selected chemicals, storage arrangement, bunding needs and local handling requirements before including the equipment in the ETP scope.
Route DAF float and biological sludge to a defined dewatering route. Spans reports typical DAF float solids content of 2–6% and identifies filter presses or belt presses where further water removal is required. A plate-and-frame filter press may be appropriate where separated sludge needs further dewatering before handling or disposal, but cake consistency, filter area, cycle time and chemical conditioning must be established from the sludge characteristics.
Require an indexed process flow, P&ID, chemical list, control philosophy, sludge balance, utilities demand, noise and corrosion information, maintenance plan, startup support and operator training. The DAF machine maintenance checklist can then be adapted to the factory’s production and cleaning schedule rather than copied as a generic schedule.
Plan for Indonesian permitting, construction and commissioning
Generic DAF performance claims are not discharge guarantees. Obtain the current applicable Indonesian discharge, sewer-entry, reuse and environmental requirements from the responsible authorities and receiving utility for the factory’s specific location. The supplied research does not establish a Medan-specific rule, and the Indian CPCB values cited in the technical source must not be applied as Indonesian limits.
Build the approval file around the proposed process, source-wastewater characterization, design flow, receiving point, effluent targets, monitoring plan and sludge-handling method. Keep each proposed treatment claim traceable to the measured wastewater and confirmed receiving requirement.
Confirm site constraints before equipment selection: footprint, inlet and effluent levels, sludge-collection access, electrical supply, compressed air, drainage, chemical storage, flood exposure and maintenance clearance. A technically adequate unit can still be unsuitable if tanks, pumps or chemical systems cannot be installed and safely maintained.
Require a factory acceptance test or witnessed performance test using agreed influent and acceptance criteria. Define site acceptance testing, operator training, startup chemicals, spare parts and remote or local support. A structured DAF troubleshooting plan should cover bubble performance, float removal, recycle pressure, chemical dosing, skimmer operation and sludge discharge during startup and normal production.
Commissioning should transfer operating documents, trained staff, calibrated instruments, a preventive-maintenance schedule and a clear escalation path for process upsets. Do not release final payment or accept the installation solely because the equipment is running with clean water.
Compare quotations using total installed cost and supplier capability
Technically comparable quotations are needed before prices can be compared. Request itemized pricing for the tank and mechanical equipment, pumps, aeration or saturation system, compressor, controls, chemical equipment, civil works, installation, commissioning, training, performance testing, warranty and spares. Identify which items are excluded; an equipment-only offer is not equivalent to an installed ETP contract.
Compare the guaranteed process basis: design flow, hydraulic loading, solids and oil loading, pressure, recycle ratio, expected effluent values, test method and acceptance tolerance. Use the best DAF unit decision framework to check that each supplier has resolved the same technical questions. If one offer omits an influent assumption, its apparently lower price is not comparable.
No Medan-specific equipment prices were supplied, so request local quotations rather than relying on an unsupported price range. The owner’s total-cost comparison should also include civil works, chemicals, power, operator time, maintenance, replacement parts and sludge disposal. The DAF cost and pricing guide can structure that review, but the final budget must come from site-specific bids.
Determine whether the supplier will characterize the wastewater, perform process design, prepare the P&ID, support permitting, train operators and provide O&M documentation—or merely deliver a machine. Ask for references in comparable applications, factory capacities and operating climates, then verify the proposed references and service support.
| Quotation element | Evidence to request before comparison |
|---|---|
| Design basis | Influent dataset, average and peak flow, contaminant loading and project-specific design assumptions |
| Equipment scope | Tagged equipment list, tank arrangement, utilities, controls, chemical system and accessories |
| Performance commitment | Test method, acceptance criteria, test influent, sample points and remedy for non-performance |
| Installed cost | Separate equipment, civil work, installation, utilities, commissioning, training, warranty and spares |
| Supplier capability | Design deliverables, permitting support, references, service response and O&M documentation |
Frequently Asked Questions
Can a Medan factory install only a DAF machine?
Yes, but only if the wastewater characterization and receiving or reuse requirements show that DAF alone provides the required treatment. DAF removes suspended solids, oil, grease, FOG and floatable material; it does not remove all dissolved biodegradable load. A DAF-only route still needs source control, flow equalization, appropriate pretreatment, chemical preparation where needed, instrumentation, controls and a sludge-disposal route. Obtain written acceptance of the proposed effluent objective before proceeding.
How much wastewater flow is needed before a DAF unit becomes economical to compare?
The research does not establish a minimum economical flow for Medan factories. Request a site-specific cost comparison based on measured average and peak flow, contaminant loading, chemical demand, civil works, available footprint and sludge handling. Compare at least the quoted DAF route against the pretreatment and biological-treatment route needed to achieve the same confirmed effluent objective; do not select from flow alone.
What should a DAF supplier include in a quotation?
The quotation should define design flow, hydraulic loading, solids and oil loading, saturation pressure, recycle ratio, expected effluent values, test method and acceptance tolerance. It should also identify included equipment, civil interfaces, utilities, controls, chemical equipment, installation, commissioning, training, performance testing, warranty and spares. The buyer should confirm whether wastewater characterization, process design, P&ID preparation, permitting support and O&M documentation are supplier responsibilities.
How do I know whether the factory needs DAF before biological treatment?
Use representative wastewater testing across production, cleaning and shutdown periods. DAF is a strong candidate when the stream contains significant oil, grease, FOG, emulsified material, fine solids or colloids that would interfere with biological treatment. Compare jar-test removal, expected chemical demand and residual COD or BOD with the biological route. DAF is not justified merely because a factory is located in Medan or because dissolved-air flotation is common in industrial wastewater treatment.
What local approvals and tests are needed before commissioning?
Confirm the current discharge, sewer-entry, reuse and environmental requirements with the responsible Indonesian authority and receiving utility for the specific site. The approval file should include wastewater characterization, process flow, design flow, receiving point, effluent targets, monitoring plan and sludge-handling method. Before handover, require agreed performance testing, site acceptance, calibrated instruments, operator training, startup chemicals, spare parts, maintenance records and a documented escalation path for process upsets.
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