Customer Case: 200 QJB Submersible Mixers for a Russian Municipal Wastewater Treatment Plant

A Russian environmental engineering contractor responsible for upgrading a municipal wastewater treatment plant selected Quzhou Zhongyi Chemicals Co., Ltd. (brand ZY) to supply 200 QJB submersible mixers for its aeration and sludge tanks. This case study explains the client's operating problem, the technical selection process and the results achieved after commissioning.

Customer Profile

The Challenge

The plant serves a mixed residential and industrial district where wastewater load fluctuates sharply between seasons and where winter temperatures fall well below freezing. The contractor's original mixers, sourced from a European brand, had reached the end of their service life and were causing three recurring problems:

• Frequent mechanical seal failures — water ingress damaged motors and forced repeated emergency repairs, each requiring tank drainage and a shutdown of the treatment line.
• Sludge sedimentation — insufficient axial thrust allowed solids to settle in corners of the aeration basins, reducing effective tank volume and increasing aeration energy demand.
• Long spare-part lead times — replacement motors and seals took 8 to 12 weeks to arrive, leaving the plant running on reduced mixing capacity.

The contractor needed a replacement supplier able to deliver a large quantity in one batch, provide complete documentation for local regulatory acceptance, and support cold-climate operation without redesigning the existing guide rail system.

Selection Process

The project team compared four suppliers from Europe and Asia against five criteria: hydraulic performance at the required tank volume, seal reliability, cold-climate suitability, delivery lead time and total cost of ownership. Our QJB series was selected after a technical review of the impeller curve, motor insulation class and seal construction.

1. Mixing duty points were calculated for each tank type and matched to five power ratings.
2. Wetted materials were specified per basin: SS304 for aggressive sludge lines, epoxy-coated cast iron for standard aeration basins.
3. Guide rail brackets were adapted to the client's existing lifting system, avoiding civil works.
4. Documentation package (test reports, material certificates, wiring diagrams, Russian manual) was agreed before production started.

Solution: Equipment Configuration

Quality Assurance Before Shipment

Every unit passed four inspection stages, and inspection records were issued with the shipment:

• Motor winding resistance and insulation resistance test
• Dynamic balancing of impeller and shaft assembly
• 24-hour continuous running test with current and temperature logging
• Double mechanical seal pressure and leak test

Packaging used fumigation-free plywood cases with foam-secured motor housings, suitable for multimodal rail transport and long inland delivery.

Results After Commissioning

The plant reported stable mixing performance through the cold season, and the contractor has since requested technical selection support for a second phase covering additional anoxic tanks.

Why the Client Chose Zhongyi

• Batch capacity of 200 units with a single delivery schedule and consistent documentation
• Adaptation to the client's existing guide rail and lifting system
• Russian-language manuals and CE documentation prepared before shipment
• Direct technical support during tank-by-tank selection

Quzhou Zhongyi Chemicals Co., Ltd. was founded in 2007 and manufactures submersible mixers, sewage pumps and progressive cavity pumps for municipal and industrial wastewater applications, with more than 80% of output exported. Contact our export team to discuss mixer selection for your next treatment plant project.