By Daniel Lakovic
Both industrial and municipal plants have a responsibility to the environment to properly process waste. Often, they need to work together to ensure that this happens. “If an industrial plant feeds into a municipal plant, it needs to ensure that toxicity levels are manageable by the municipality,” said Frank Scriver, of Flottweg Separation Technology Canada, ULC. “Municipal plants then have the highest responsibility, since the effluent from them must be ‘clean’ enough to prevent harm to the environment.”
There are several trends in waste handling that can create viable solutions for savings in production time, operational costs and environmental strain.
There are several operational costs that can impact a wastewater plant, including the transport of solids. “After solids are separated from the liquid, the liquid is further treated, then disinfected to a level that ensures safe reintroduction into the environment,” Scriver said. “In some cases, this effluent is safe enough for human consumption, although many still cringe at this thought.”
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The solids, however, will either be transferred to a landfill, or, if treated further, can be used as fertilizer. There are even opportunities to use biosolids as a source of energy when used as fuel for generators. “Since these solids need to be transferred, the overall mass and weight plays a huge role in the cost of the transfer,” Scriver added. “Essentially, water becomes the enemy. The drier the biosolids, the lower the transfer costs.”
New technology innovations
Savings calculations require data, and most plants effectively keep these records. “Often, these are facts that are used to judge how well the plants are being managed,” Scriver explained. “However, there are occasions when new technology emerges that requires rethinking. Some technology innovations have such a quick return on investment (ROI) that the investment becomes an easy choice. These could be chemistry, process, or mechanical innovations.”
Many plants are continuing to automate their processes. “Machines communicating with other machines is a trend that will continue to grow,” Scriver said. “Computers are making adjustments based on process sensors, which ensure optimal operations. This requires manufacturers of varying equipment to work together to find solutions that will optimize a plant’s efficiency. For example, centrifuges have been regarded as costly to operate. A misconception is that the high-speed spinning wears the equipment quickly. However, when looking to separate a liquid from a solid there is no better technology that compares to the containments, efficiency and consistency of this machine.”
Case study: Food processing company
For JTM Food Group, a family-managed food processing company, producing low-fat, low-calorie products in an environmentally responsible, sustainable and energy-saving manner is the top priority. Thanks to an upgrade to a three-phase centrifuge from Flottweg, JTM can separate its wastewater into grease, water and solids in one step during production. This allows the company to achieve a cleaner fat content, less wastewater and drier solids than ever before.
For JTM, that means cost savings due to reduced wastewater volume and added profits, since they can reuse solids as animal feed.
“We needed to reduce the amount of water that we send to the city,” said Jerry Cramer, process consultant for waste treatment at JTM. “And, we needed to make that water quality as good as we possibly could.”
Dewatering removes materials that are contaminating the water, so JTM can either reuse them or recover them for some other purpose.
In three-phase separation, it is possible to separate two liquid phases from one solid phase at the same time. The different densities of the (immiscible) liquids and the solid mean that all three phases can be discharged simultaneously using Flottweg’s Tricanter®.
Cast study: Wastewater treatment plant
Solvay has a wastewater treatment facility and two chemical plants at one of its locations. Three other chemical plants feed into the activated sludge wastewater treatment facility, making it difficult to create a consistent sludge. The five sites produce around 11 million litres of wastewater per day.
“We have a lot of different batches here which change day-to-day, and month-to-month,” said Brian Smith, Solvay’s maintenance and wastewater treatment superintendent. “This makes it difficult to keep a healthy biomass. The biomass is constantly changing. We see many different food groups. The food can swing quickly, which makes it very difficult to develop a consistent sludge.”
This is a common challenge for treatment plants when there are batches from multiple sources and very little, if any, equalization.
To make a consistent sludge requires a consistent waste. “If everyone sends a consistent waste, then the bacteria would acclimate to it,” Smith said. “You could grow healthy bacteria that would settle. But when you constantly change the pH and the chemical feed, you have some bacteria that are dying and others that are increasing in population. This type of sludge is extremely difficult to dewater.”
When the solids level rises in a wastewater treatment plant, costs also rise. In the winter of 2017, Smith connected with Flottweg Separation Technology and was able to work within its pilot program on a rental agreement for centrifuge equipment.
“The pilot unit originally came with a solid scroll; it was then exchanged for an open bodied (Xelletor) scroll,” Smith said. “We saw a huge improvement. The pilot unit was giving us solids at 19% – 20%. It was easy to run. We hit the start button and it began producing product right away. We began to run the open bodied (Xelletor) scroll from April to August and it was a step change. The product was flaky, and it was much easier to keep the centrate clean. It was at least 21% solids. That one or two percent makes a physical change in the way the sludge looks and the way it behaves.”
The Flottweg Separation Technology centrifuge system allowed the Solvay wastewater treatment plant to reduce man hours used with the dewatering equipment, reduce operation time and tons of landfilled material, increase sludge consistency, and reduce energy.
This system allowed Solvay to decrease operation time from 24/7 with full-time dedicated operators, to just one 12-hour shift per day. The centrifuge system decreased the need for additional manpower and also reduced the risk of injury for the operators.
The plant no longer needs to add fly ash to the centrifuge, which saves the cost of fly ash, hauling cost and tipping fees because the end product is lighter.
In total, the plant was able to see a ROI within a few months. After the first year in operation, the Flottweg system proved its worth by providing Solvay a net annual savings of more than $214,000. This number includes costs for ash, ash transport, landfill transport, disposal, polymer, rental, rental labour, rolloff boxes, rolloff truck, plastic liner, maintenance and electrical.
Case study: Municipal wastewater plant
The Greenway Wastewater Treatment Plant is the largest plant in the City of London, Ontario. It has a designed capacity of 170 million litres per day and a peak capacity of 255 million litres per day. It takes approximately two-thirds of the city’s wastewater flows.
Greenway’s disposal process is incineration. The treatment plant now utilizes Flottweg centrifuges to dewater biosolids to a solids content of about 26%. Additionally, ancillary fuel is not needed anymore, which results in a savings of nearly $900,000 per year.
“Depending on the level of water content in the sludge, more energy is required for more water content, and less energy is required for less water content,” said Randy Bartholomew, Greenway’s supervisor of operations. “Because the level of solids was much lower with the belt filter presses, it required us to use auxiliary fuel to maintain that energy level and the temperature in our fluidized bed.”
In 2012, Greenway installed three Flottweg C7E units. The process is operating 95% of the time, and two of the units will be running at all times. These three machines are individually designed to accommodate 1,200 litres per minute of liquid flow, or 1,700 kg per hour of mass flow.
“With the centrifuges we can bring the solids content up to a level where we don’t have to use auxiliary fuel to maintain the temperature,” Bartholomew explained. “It runs without that fuel. In addition, polymer consumption actually is probably about 75% of what we originally anticipated.”
The biggest cost savings for the wastewater treatment plant came with the reduction in auxiliary fuel (natural gas).
“Biosolid dryness can greatly affect overhead,” said Geordie Gauld, division manager at the Greenway plant. By reducing dryness from 24% to 25%, the plant was able to burn the biosolids in incinerators without the aid of natural gas. They are currently treating approximately 17,000 dry tons of biosolids per year.
The Greenway plant hauls leftover ash to a nearby landfill. Not every plant utilizes incineration processes, however. Some skip burning and haul dewatered sludge cake directly to a landfill. In these instances, the transportation cost is heavily weighed against the dryness of the cake.
The changeover from belt presses to centrifuges was not entirely seamless. Polymer consumption increased, but the added cost was more than offset by gas savings. Also, centrifuge parts tend to be more expensive than belt press parts. This, however, is offset by the fact that there are fewer wear parts and therefore repair is much easier.
With the transition to Flottweg’s centrifuges, the Greenway plant was able to meet the demands of its operational management, as well as the low downtime desired by maintenance personnel. The system has helped them reduce costs and simplify operations.
Daniel Lakovic is with Flottweg Separation Technology Inc. This article appears in ES&E Magazine’s August 2019 issue.