Submersible Remotely Operated Vehicle Cleaning System

Automated closed-loop ROV cleaning for pulp and paper covered lagoon

Customer

2–5 million gallon pulp and paper anaerobically digested covered lagoons in southeast Ohio, USA

Problem

The customer uses the covered lagoons to reduce or treat the influent chemical oxygen demand and biochemical oxygen demand from the pulp and paper production facility. The effluent from the two-stage lagoon process is then processed to 2–10 million gallon aerated lagoons and finally discharged to the local watershed. The customer’s current aerated lagoons are not large enough or capable of treating the influent directly, limiting their ability to take the covered lagoons out of service for cleanings or solids removal. The primary covered lagoon was 95% full of solids, and the second covered lagoon was 65% full of solids. The solids accumulation was causing short-circuiting of the treatment process and affecting the aerated lagoon’s ability to treat wastewater from the pulp and paper production. There was a potential for violating the National Pollutant Discharge Elimination System discharge permit if they did not address the solids accumulation in the AD covered lagoons.

Potential Costs

The customer received proposals upwards of $250,000 to remove and replace the cover and another $400,000-plus to bring in dredging and dewatering equipment to remove the solids from the primary covered lagoon. The customer might also have needed to rent a mobile membrane bioreactor system at $35,000 per month to treat the influent during cleaning and solids removal.

Solution

Bristola proposed using a 24" submersible ROV to remove and clean the covered lagoon. Two open-top weir tanks and one belt filter press were used to remove and dry the solids between 20–25% total solids. The supernant and filtrate/wash water were returned to the covered lagoon.

Execution

The submersible ROV was deployed via a 30 inch manway. Each covered lagoon contained three manways. A telehandler and winching cable were used to deploy the submersible ROV. The solids were injected with neat polymer to facilitate settling before going to the open-top weir tank. The supernant on top was pumped back to the lagoon, while a rotary lobe pump on the BFP removed the thickened/settled sludge. The sludge was processed to a Kromline 2.5 meter BFP. The SRCS processed between 180,00 and 220,000 gallons per day. The percent solids from the cake ranged from 20%–25% TS. A total of 75–120 yards per day were taken to the local landfill for disposal.

Project Costs

The project cost was $300,000 for operating the SRCS system on-site for 30 days and $30,000 dollars for mobilization of pumps, BFP and other ancillary equipment.