Sludge Dewatering

During the sludge dewatering process, water is removed from the sludge to reduce its volume and weight for disposal or further treatment. No matter what methods are used for sludge dewatering, it is important to finetune the process in order to minimise both the environmental and economic cost.

Full monitoring of the dewatering process

Sludge dewatering is performed using a wide variety of technologies. For processing urban wastewater sludge, we often see centrifuges, belt filter presses or a screw press. Iron water is often thickened using gravity thickening.

Specifically for centrifuges or dewatering presses, we have 4 sensors available for these 3 locations (not all are required), for full monitoring of the dewatering process:

1. Sludge inlet: Sludge concentration of thickened sludge

2. Centrate:

   1. Measuring residual polymers in centrate

   2. Total Suspended Solids (TSS) in centrate

3. Sludge Cake (DS% in dry cake)

For usage in other sludges (eg. iron water sludge), we have monitoring solutions that can be free hanging in a gravity thickening bassin.

All of these parameters have specific challenges, that can be attacked by the innovative OLPAS Technology using ultrasound instead of the traditional optical or microwave technology.

Keep an eye on dosing effectiveness by measuring solids in sludge during different stages of sludge dewatering.

Olpas sensors in this application do not need automated mechanical cleaning. No wipers. No pressured air. And only limited preprocessing of the centrate in a flow-cell or preprocessing unit.

Sludge concentration at the inlet [1]

The sludge concentration measurement at the inlet of the dewatering unit is vital to determine the amount of polymers to add and the energy usage of the dewatering process. An accurate measurement that swiftly follows the real concentration trend allows the control system logic to adapt the added polymer content or sludge flow-rate.

Other sensors for measuring sludge concentration

Current state-of-the-art optical sensors fail to measure the concentration accurately in changing conditions, due to their dependence on the optical parameters of the sludge. Furthermore, fouling is present after a few days of operation that cannot be fully reversed by the fault-prone mechanical wipers. In between maintenance events, optical sensors in sludge tend to drift and need frequent validation (and sometimes even re-calibration) using lab samples.

The well known brands of microwave based sensors, are generally expensive and hard to install with a cost that becomes higher when the diamter of the tube increases.

Olpas sensors are not impacted by optical parameters, have a high tollerance for (bio)fouling or precipitation, and are easy to install inline.

Quality control of centrate or filtrate [2 & 3]

The quality of the centrate is a more subtle indicator of the dewatering process efficiency.

1. A high suspended solids (TSS) content in the centrate increases waste water processing costs upstream in the plant and is an indicator of an inefficient dewatering process.

2. A clean centrate with a large polymer content is an indicator that polymer dosing is not scaled correctly in relation to the incoming solids content.

   
   

Both measurements combined allow to optimize centrate quality without reducing dewatering performance. A good set of sensors with low drift and long maintenance intervals are required to make sure dewatering performance is kept continuously on point.

"Centrate is almost never monitored actively. Not because it does not provide important information, but because it is extremely hard to do. Untill now. Olpas changes this paradigm and makes monitoring centrate possible and economically feasible."

Sludge cake [4]

The goal of a dewatering solution is often to obtain a sludge cake with an optimal amount of moisture present while consuming as little polymers and energy as realistically possible.

Using a set of sensors as described before, sludge cake quality can be expected to be kept constant.

Gravity thickening or iron water sludge

For thicking of Iron Water sludge (Ferric hydroxide), gravity thickening is often used. Also in these processes, Olpas sensors are usefull. We have sensors available for freehanging installation in a iron sludge silo.