Due to company strategic adjustments, I haven’t been to a sludge dewatering project site in a long time. However, one day last month, I had the opportunity to visit a wastewater treatment plant to inspect the renovation of the dewatering machine room. I also hoped to take this opportunity to understand the current status of sludge dewatering in the municipal industry.
The plant was initially built in 2016 and put into operation in 2019, with a current capacity of 30,000 m³/d. Expansion began in 2020, with an additional capacity of 60,000 m³/d, bringing the total designed water volume to 90,000 m³/d. The long-term total capacity is 120,000 m³/d.
The upgraded processes are as follows:
- Wastewater Treatment Process: Coarse Bar Screen &Lift Pump Station → Fine Bar Screen & Cyclone Grit Chamber → Distribution Well → Hydrolysis Acidification Tank → Modified Bardenpho Process (AAO+AO) → Secondary Sedimentation Tank → High-efficiency Sedimentation Tank → Denitrification Deep Bed Filter → Ultraviolet Disinfection → Discharge.
- Disinfection Process: Ultraviolet Disinfection Process.
- Sludge Treatment Process: Belt Filter Press for Sludge Dewatering.
- Deodorization Process: Biological Deodorization Process.
Effluent Standards: CODcr≤30mg/l, BOD5≤6mg/l, SS≤5mg/l, NH3-N≤1.5mg/l, TN≤12mg/l, TP≤0.3mg/l.
The plant’s dewatering machine room was designed to accommodate a long-term capacity of 120,000 m³/d. Therefore, the new dewatering machines added during this renovation are located within the existing machine room. Our focus was on examining the current state of the existing machine room and the operational status of the existing dewatering machines.
The factory currently has 2 sets belt filter presses with a bandwidth of 2.5m, manufactured in 2018.
Operational Data Shows:
Unit #1: Sludge inlet pump frequency: 15Hz, dosing pump frequency: 48Hz;
Unit #2: Sludge inlet pump frequency: 16Hz, dosing pump frequency: 48Hz;
The rated flow rate of the sludge pump is 60 m³/h, which translates to approximately 18 m³/h of displayed flow rate, basically consistent with the flow meter reading.
Sampling sludge, after testing, showed an inlet sludge moisture content of 99.2%.
The measured moisture content of the sludge cake after dewatering by the existing belt filter press was 84.6%.
The equivalent dry sludge yield is 140 kg/h. Considering the recovery rate, the yield is surprisingly low.
The reasons for the low yield will not be analyzed here.
Based on the actual sludge conditions on site, a 2.5m wide belt filter press should have a processing capacity of at least 50m³/h and a dry sludge output of >400kg/h.
Even though the customer later added flushing pipes in an attempt to improve the cleaning effect of the filter belt, the sludge discharge rate remained unsatisfactory.
Considerations:
1. If we estimate the actual water volume at 25,000 m³/d and assume a residual sludge volume of 4,000 kgDS/d, the dewatered sludge volume would be approximately 26.7 t/d (85%). Based on the current actual processing capacity of 140 kg/h per unit, two units would need to operate for 14.3 hours. However, if we aim for a design capacity of 400 kg/h, only one unit would be needed, operating for 10 hours.
Assuming each unit consumes 20 kWh of electricity at a cost of 0.8 yuan/kWh, the annual electricity cost savings would be (14.3 × 2 – 10) × 365 × 20 × 0.8 = 108,600 yuan.
If the moisture content could be reduced to 80%, the dewatered sludge volume could be reduced by 6.7 t/d. At a disposal cost of 250 yuan/t, the savings would be 6.7 × 365 × 250 = 611,300 yuan. Adding in the costs of chemicals, water, etc., isn’t the result somewhat unbelievable? 2. This situation at the factory is a common phenomenon in the industry. So why does this happen so frequently? This reflects the overall level of our industry, not just in terms of technology, but also due to other reasons, which I won’t elaborate on here.
3. Countries around the world have introduced relevant sludge treatment measures, which demonstrates the importance they attach to sludge treatment. The key question is how to effectively implement these measures.
Actually, we don’t lack good technology, or even good equipment. So what do we lack?
Zhaolie Environmental Protection – Not only providing high-quality equipment, but also trustworthy full-process after-sales service.
