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,
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.”
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
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.
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,