Vast Improvement in sludge dewatering through chemistry and SMART technology

21/12/2016 Success story

Challenges at optimizing sludge dewatering are not atypical at many wastewater treatment plants. Kemira recently assisted Renda Environmental with problems it had in 2014 when dewatering anaerobically digested sludge from the Village Creek Wastewater Treatment Plant in Arlington, Texas.
Village Creek’s wastewater flow averages 100 million gallons per day, and initial sludge flows to the Renda Environmental dewatering facility averaged 1,000 gallons per minute. In late 2014, the Renda facility started to suffer from deteriorating dewatering performance. Cake solids were wetter and malodorous than before, which led to increased hauling costs and complaints by the residents due to the odor. Additionally, struvite started to build up on in the sludge grinders and on the belt filter presses, increasing the maintenance costs.
Value-added approach with Kemira’s SMART control and monitoring for solids to liquid separation
Kemira Application Manager Tafadzwa “Tee” Mariga notes that the client’s problems were due to the Village Creek wastewater treatment plant starting to receive sludge that contained poly-aluminum chloride from smaller local wastewater treatment plants. In this situation, the sludge held more water than earlier, when the local plants had used ferric sulphates.
“Our team came to the conclusion that the best solution was a combination of appropriate chemistry and SMART technology. It is the specific combination and way of dosing inorganic coagulants, in this case an iron salt, with the organic flocculant (polymer) that resulted in an improved dewatering performance, odor control and struvite control,” notes Tee
To turn around the challenging situation, preciseness and effectiveness of dosage was very important. Kemira introduced a flow-paced dosing of chemistries to account for variances in the sludge flow. A real-time total solids meter was installed prior to the coagulant application point for an option to dose the chemical on a pound per dry tonne of sludge basis with the sludge flow taken into account. A second real-time monitoring device was placed after the iron salt feed to dose the polymer accordingly.
“Our technologies allowed for the plant to dose chemicals as per demand. This SMART chemical treatment of the sludge enables the optimization of the chemical consumption and always delivers the best dewatering performance, even if the input sludge properties vary over time.” Tee says.
To further increase the effectiveness of dosage the Kemira team also put in place a customized chemical distribution technology for instant mixing and reaction with the sludge in the post digester holding tanks. Kemira storage tanks, containment and a pump system were installed onsite. An additional tank level monitor sends low level notifications to the customer and Kemira customer service so as to schedule the next chemical delivery.  Kemira’s exclusive KemConnect software, monitors the entire process, while sending summarized reports on sludge and chemical flows, trends and levels. It can also monitor the real-time solids trends and thus visualize continuously the dewatering performance.
Remarkable savings and process improvements
The solution proved to be very effective, and results were quickly available.
“The beauty of dosing the right chemistry combination with a controlled program is that you see the benefits quickly. The belt press cake went from being sloppy to crumbly once the chemistry went through the system. It worked like magic,” Tee recalls.

Showing significant improvement, the site increased the belt press cake solids by 5%. Renda’s hauling costs were remarkably decreased, considering that the drier sludge cakes made it less expensive to transport them. In addition, struvite build-up on belt presses was reduced, which diminished the maintenance costs. Since the start of this SMART dewatering, Renda has had no odor complaints, which is saving the company significant costs as each odor complaint reported costs at least $2000.
“The advantage of the value-added program is that the chemistry combination allows the selection of some benefits over others. For example, Renda had an option to keep the polymer dosage the same and the coagulant allowed them to increase their belt press throughput by at least 20%. This enables savings in labor, electricity and equipment run time.” Tee concludes.
Other benefits included reduced belt press filtrate ortho-phosphate levels (over 90%). The belt press filtrate is returned to the head works of Village Creek and so this reduction has had a positive effect on the overall plant treatment process. The plant managers claim that they have witnessed improved settling rates in their primaries and that they are treating less water. The improved filtrate quality has also qualified Village Creek to sell their reuse water to the local airport for machine cleaning.
Customer benefits
  • Performance improvement - Up to 5% total solids increase in cake solids, reduced odors, struvite control
  • Efficiency improvement - 20% increase in belt filter press throughput at the same polymer dosage
  • Cost savings - 10%, plus additional savings from hauling, struvite clean outs, wasted polymer from overdosing,
    disposal and odor fines.

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