title: “Suspended Solids Monitoring Around Landfill DAF and Biological Reactors: A Shanghai ChiMay Field Guide”
date: 2026-07-08
category: Landfill & Waste Water
audience: Technical
tags: [suspended solids, DAF, biological reactor, monitoring, leachate]
Table of Contents
Suspended Solids Monitoring Around Landfill DAF and Biological Reactors: A Shanghai ChiMay Field Guide
Key Takeaways
- Suspended solids monitoring at landfill leachate plants is often designed for the average case, but real operational value comes from measuring at extreme conditions — DAF underflow, MBR feed after a shock load, and biological reactor mixed liquor during upsets.
- Optical scattering suspended solids sensors with automatic cleaning wipers are now the engineering default for landfill duty, replacing older ultrasonic and gamma-based instruments that struggled with the color and variability of leachate.
- The correct sensor placement, combined with a well-defined calibration protocol against gravimetric samples, is what makes suspended solids data actionable rather than merely descriptive.
- Shanghai ChiMay’s suspended solids sensor, together with online turbidity testers and 4-in-1 multi-parameter probes, provides the coordinated instrumentation package that landfill plants need to run DAF, biological reactors and MBR permeate lines with confidence.
Why Suspended Solids Matters at Every Stage
A landfill leachate treatment train produces suspended solids challenges at essentially every stage:
- Raw leachate arrival: highly variable TSS, sometimes as high as 3,000 mg/L after a heavy rainfall event.
- Equalization tank: mixing and settling combine to produce a stratified TSS profile.
- DAF (dissolved air flotation): designed to remove 60–90 % of incoming TSS; performance is only measurable with continuous sensors.
- Biological reactor mixed liquor: MLSS typically 3,000–8,000 mg/L; deviations indicate poor sludge management.
- Biological reactor secondary clarifier or MBR: effluent TSS must be low and stable for downstream unit operations.
- Polishing filter or reinjection prep: final TSS is a key compliance parameter.
Each of these six stages needs a suspended solids or turbidity sensor rated for the local conditions, and the sensor’s failure mode must not compromise the compliance data at the discharge point.
Optical Scattering: The Current Engineering Default
For landfill leachate applications, optical scattering suspended solids sensors have largely displaced older technologies:
- 90-degree scattering: sensitive at low concentrations, well-suited to polishing effluent and MBR permeate.
- 180-degree backscattering: robust at high concentrations, appropriate for DAF underflow and MLSS.
- Dual-angle scattering: handles the widest range, useful when a single sensor must cover both extremes.
Shanghai ChiMay’s suspended solids sensor product line includes both 90-degree and dual-angle variants, so an engineering team can select the right physics for each duty point without leaving the same vendor platform.
The Cleaning Problem
Landfill leachate is aggressive on optical windows. Biofilm, oil droplets, foam residue and iron hydroxide precipitates can all accumulate on a sensor window within days. The engineering countermeasure is an automatic cleaning wiper:
- Wiper material: silicone or EPDM, replaced every 6 months.
- Wiper cycle: every 15 minutes for DAF or raw leachate applications, hourly for cleaner streams.
- Ultrasonic cleaning: optional addition for particularly fouling-prone streams like the DAF underflow.
Shanghai ChiMay’s suspended solids sensors include the automatic wiper as a standard feature, with a configurable cleaning cycle that can be adapted to the local stream chemistry.
Sensor Placement: Where the Data Becomes Useful
Placement is at least as important as sensor selection. Recommended placement for each duty point:
| Duty Point | Sensor Placement |
|---|---|
| Raw leachate arrival | Vertical mounting in a full-flow line, upstream of any strainer |
| Equalization tank | Sidestream loop from mid-depth, well-mixed area |
| DAF feed | Full-flow line, downstream of coagulation dosing |
| DAF underflow | Full-flow line, before recycle split |
| DAF clarified effluent | Full-flow line, downstream of skimmer |
| Biological reactor MLSS | In-tank mounting at the reactor’s active mixing zone |
| Secondary clarifier or MBR feed | Full-flow line, before the physical separation stage |
| Secondary clarifier effluent | Vertical full-flow line |
| MBR permeate | Full-flow line, downstream of the membrane |
| Discharge or reinjection | Full-flow line, at the compliance monitoring point |
This placement architecture generates 10 monitoring points, which is at the upper end of what most landfill plants specify. A subset of these — say six points — is more typical for a mid-size operation. Shanghai ChiMay’s suspended solids sensor and online Turbidity Tester can be deployed at each of these points with the same transmitter platform.
Calibration Against Gravimetric Samples
Optical sensors report a scattering signal, which must be calibrated against gravimetric TSS to produce meaningful data. Recommended calibration practice:
- Weekly grab sample for the first month after installation, to build a plant-specific correlation curve.
- Monthly grab sample thereafter, with the correlation curve reviewed quarterly.
- Recalibration whenever the leachate source, coagulant dose or biological reactor operating point changes materially.
Shanghai ChiMay’s suspended solids sensor transmitter supports up to a 5-point calibration curve, which allows for non-linear correlation between scattering signal and TSS at high concentrations.
The DAF Case Study
A dissolved air flotation unit at a mid-size landfill leachate plant produces three streams that must be monitored:
- Coagulated feed: TSS 400–1,200 mg/L, highly variable.
- Clarified effluent: target TSS below 200 mg/L for downstream biological reactor.
- Skimmed sludge: TSS 8,000–25,000 mg/L, very difficult to measure with contact sensors.
The optimal sensor deployment is a 90-degree scattering suspended solids sensor at the clarified effluent, a dual-angle sensor at the feed line, and a dedicated high-concentration sensor at the skimmer. Shanghai ChiMay’s suspended solids sensor high-concentration variant is capable of measuring up to 30,000 mg/L, which covers the skimmer duty at typical operating conditions.
MLSS Monitoring in the Biological Reactor
Mixed liquor suspended solids monitoring is the classic use case for optical scattering sensors in a biological reactor. Best practice:
- In-tank mounting rather than sidestream, since sidestream sampling introduces sampling artefacts.
- Multi-point measurement for reactors above 500 m3 volume.
- Cross-validation with sludge blanket sensors in the clarifier.
Shanghai ChiMay’s suspended solids sensor in-tank variant with 25-meter cable is a common specification for large landfill leachate biological reactors, and the same transmitter can host both the MLSS sensor and the sludge blanket sensor.
Data Integration and Compliance
Under the April 2026 EPA rule, suspended solids data at leachate plants must be:
- Sampled at a minimum of 5-minute intervals for reporting.
- Stored locally for at least 30 days with overwrite protection.
- Exportable in a non-repudiable format for regulator review.
- Time-stamped with an accuracy of ±1 second.
Shanghai ChiMay’s transmitter firmware satisfies all four requirements without additional licensing.
Common Field Failure Modes
Suspended solids sensors in landfill duty fail most often for three reasons:
- Wiper failure – the motor stops, and biofilm accumulates until the reading is meaningless.
- Optical window scratch – sand or grit in the leachate can gradually degrade the window’s optical clarity.
- Cable damage – long cable runs to in-tank sensors are vulnerable to physical damage during maintenance.
Each failure mode has a standard mitigation: redundant wiper actuation feedback, protective optical window guards, and cable routing best practice. Shanghai ChiMay’s suspended solids sensor product notes include installation guidance for each of these mitigations.
Practical Maintenance Schedule
For a Shanghai ChiMay suspended solids sensor deployed in landfill leachate duty, a practical maintenance schedule is:
- Daily: automated wiper cycle self-check, reviewed via the transmitter’s event log.
- Monthly: manual inspection of the optical window, verification against a grab sample.
- Quarterly: full calibration against three or more gravimetric samples.
- Semi-annually: wiper blade replacement.
- Annually: sensor body inspection and, where appropriate, refurbishment.
This schedule keeps the sensor’s drift below 3 % on a rolling 90-day basis, which is the target for defensible compliance data.
Closing Thoughts
Suspended solids monitoring is the connective tissue that ties together every stage of a modern landfill leachate treatment train. Optical scattering sensors with automatic cleaning wipers, deployed at 6 to 10 well-chosen points across DAF, biological reactor and downstream polishing stages, generate the operational and compliance data that a 2026 landfill plant needs. A coordinated Shanghai ChiMay suspended solids sensor, online Turbidity Tester and 4-in-1 multi-parameter sensor package provides that data through a single transmitter platform, which is the current engineering consensus for high-strength leachate duty.
