Markland Specialty Engineering Ltd.

- Automatic Sludge Blanket Level Detector


This is Markland’s most comprehensive sludge blanket level detector, offering automation of desludge pumps at both high and low set points and providing a LED readout, yet versatile enough for use in obstructed or constricted areas.

Measure, monitor and control the sludge bed depth

  • In diverse clarification processes: silt or biosolids in primary and secondary sludge, backwash sludge from sand or membrane filters, resin beds in intake water softeners, settled mud levels in tanks, settled fly ash from scrubbers, and more.

Meet the needs of your unique application

  • Slim profile and high-intensity infrared light are ideal for obstructed or constricted areas, such as inclined plate lamellas.

No calibration required

  • Beam intensity of the LED-phototransistor sensors automatically adjusts to accommodate thick or thin biosolids concentration and even light flocs.

Complement other treatment processes

  • In DAF units, the detector can adjust surface skimmer speeds to match variations in the thickness of the floating sludge layer. In SBRs, it can control the decant valve to minimize cycle times.

Automatically maintain preferred liquid-solids interface levels

  • Help prevent carryover.

Optimize silt or sludge feed density for enhanced dewatering

  • Maximize water removal. Avoid pumping large volumes of thin sludge. Improve outflow for reuse.

Reduce energy use, wear-and-tear on pumps, and downtime for maintenance

  • Program desludge pumps to run only when necessary rather than at timed intervals.

Get answers when you have questions

  • Technical assistance is factory-direct from the designers and manufacturers of this sludge blanket level control equipment.

Used wherever solids are separated from liquids:

  • Municipal water and wastewater treatment plants
  • Primary and secondary clarifiers (gravity settlers)
  • Inclined plate clarifiers / separators (Lamellars ®)
  • Dissolved air flotation (DAF) tanks (floating bed)
  • Decanting tanks / Decanting control
  • Industrial process + Wastewater clarification
  • Sequential batch reactor (SBR)
  • Batch processes
  • Settlement tanks

  • LED beam automatically adjusts its intensity to detect settled sludge blanket and supernatant interface levels in thick or thin sludges, or in light flocs
  • sludge level interface detection is not distorted by the curved walls of lamellar® tanks
  • advanced self-diagnostics
  • ultra high intensity infrared beams
  • automatic beam intensity control
  • 4 – 20 ma output linear with sludge interface level depth
  • high & low sludge blanket depth set-point relays

A vertical Probe, submerged in the settlement tank, contains 64 infrared high intensity LEDs stacked vertically, which shine horizontally across a probe gap to 64 phototransistor detectors. This gap contains either liquid or sludge. The 64 pairs are sequentially scanned to locate the sludge bed. Beam power intensity is automatically adjusted to accommodate different sludge and overlying liquid concentrations. At its highest power level, the beam will shoot through your hand, you could count the bones, but there is not hazard since the beam is only on for a few microseconds. This high intensity beam easily penetrates fouling on the probe’s windows, and as long as the solids in the probe gap are high relative to the solids in the scum layers on the windows, the meter continues to read correctly. Eventually, the probe has to be removed and given a wipe with a soft cloth.

Process Control

Automatic desludging yields thicker sludge than timers or manual methods, and reduces sludge disposal or processing cost. A desludge pump can be operated automatically from the Low Set-Point Relay along with a Pump Run Interval Timer, and the High Set-Point used as an alarm for excessive sludge depth. Alternatively, the desludge pump can be turned ON at the High Set-Point and OFF at the Low Set-Point, or the 4-20 ma output can be used for continuous variable speed drawoff. The 4-20 ma output can link the sludge blanket level meter to your computer for centralized process control.

Pause Switch Uses

An externally located switch, with a pair of Normally Open contacts, can be connected to act as a “Pause Switch”. When these contacts close, the Markland transmitter freezes its last reading, and the LCD displays “METER DISABLED HOLDING LAST READING”. This feature is used for a batch mix process to disable the meter during mixing. It is also used to lock out the meter, when the probe is tipped up by a traveling scraper. Both of these uses are illustrated in the accompanying diagrams. When the pause switch reopens its contacts, the sludge blanket level meter waits 30 seconds for the sludge to settle down before resuming normal operation.

  • Materials:
    • Probe: PVC
    • Mast: PVC Pipe
    • Clamp: Stainless Steel & Polypropylene
    • Cable: Vinyl Jacketed
    • Enclosure: Fiberglass Body & Clear Plastic Cover
  • Dimensions:
    • Probe
      • Overall Length: 1330 mm (52¼ in.)
      • Active Element: Length 1219 mm (48 in.)
      • Cross Section: 64 mm (2½ in.) x 38 mm (1½ in.)
      • Gap: 25 mm (1 in.)
      • Mast: 3.5 meters (12ft.), 1 in. Sch. 80, shipped in 3 pieces with fittings
  • Enclosure:: Width 343 mm (13½ in.) Height 229 mm (9 in.) Depth 200 mm (7 7/8 in.)
  • Cable Length: 15 meters (50 ft.) pigtail supplied (measured from top of Probe). Maximum cable length 150 meters (500 ft).
  • Order extra cable separately if pigtail length not sufficient
  • Element Spacing: 64 pairs infrared LED/Phototransistor, spaced vertically on 19 mm (¾ in.) centers. Dual Model has 128 pairs
  • Accuracy: ± 2cm (± 1 in.)
  • Bottom Offset: Adjustable, 0-700 cm or in. (NOTE: For ‘-DAF’ & ‘-UD’ types this is Top Offset)
  • Depth Units: Selectable, inches or centimeters
  • Temperature: Maximum 50°C (120°F)
  • Power: 110/220 VAC, 220/240 VAC, 50/60 Hz (advise with order). 10 watts
  • Outputs:
    • Liquid Crystal display (LCD) 2×20 Digit Alphanumeric
    • 4 – 20 ma output signal, linear with sludge interface level
    • Two DPDT, 5 Amp, Relays, independently adjustable set-points
    • RS – 232 Serial Port
    • RS – 485 Serial Port (Optional)
  • Models:
    • 602: Reads sludge depth up from tank bottom
    • 602 – UD: Reads sludge blanket location down from liquid surface
    • 602 – DAF: Reads sludge/liquid interface in Dissolved Air Flotation thickeners
    • 602 – LP: Special model for Drinking Water Plant upflow clarifiers where overlying water is very clear & sludge is thin (consult factory for further details)
    • 602 DUAL &
    • 602-DUAL-UD: Uses 2 probes, one mounted 48 in. (122 cm) above the other to give 96 in. (244 cm) continous span
  • Approvals:
    • CSA Approved and CE Conformance

The graphics below demonstrate the Markland difference. With Markland’s Fixed Sludge Level Control Equipment, you only pump when necessary, resulting in no overflows, no unnecessary pumping and running the risk of pumping water with sludge.

Light Desludging

LIGHT sludge loading can allow a timer to pull a core hole and pump water out the bottom.  The Automatic Sludge Level Detector does not turn on the desludge pump until it is required, and the sludge level is maintained within the high and low set-points.

Heavy Desludging

HEAVY sludge loading can overwhelm a timer-controlled desludge pump, allowing sludge to slip over the top, while the Automatic Sludge Level Detector maintains the sludge level within the high and low set-points.