Senior Design Project Improves Water Treatment Technology

4/25/2012

Senior Design partners and Environmental Engineering majors Chelsea Bajek, Rebecca Pianese and Tina Singh have created a more cost-effective form of a waste treatment process, on display at today's Stevens Innnovation Expo. Called a “split stream leaching process,” it extracts heavy metals and phosphorus to create Class A sludge, which is sludge in its required form to be considered an approved fertilizer source. 

“People hear the word ‘sludge’ and automatically associate it with something bad,” explains Bajek. “But sludge from waste can be useful.” 

The United States is one of the world’s top producers of sludge. Sludge, which is a solid, semisolid or liquid residue left after sewage and waste is treated at a sewage plant, can be used for practical purposes if treated correctly. Such a substance is considered a renewable resource and is most commonly used in wastewater treatments or turned into a biosolid that acts as a government-approved and nutrient-rich fertilizer.

The group’s idea is to split incoming sludge loads from municipal waste plants into two proportioned parts and treat each part with either a hydrochloric acid or sodium hydroxide extraction dosage. This process will remove heavy metals and phosphorus. The acid-treated sludge and base-treated sludge, now having been removed of all necessary impurities, are then mixed in order to neutralize the material and make it safe to use.

The problem could not be solved by simply extracting heavy metals and phosphorus in landfill sites containing sludge—it is also important that such an operation be performed in a cost-conscious manner. 

“Generally, an acid extraction technique is used,” said Pianese. “In this, you add the acid and then add a buffer, but this process involves a lot of chemicals, and with that comes a lot of expense.” 

By completely eliminating a buffer in sludge treatment, municipal waste plants will save a considerable amount of money.

The split-stream process will produce the same neutralizing effect that a buffer will with the use of a strong acid and base. The group’s project has the same result as current treatment techniques but uses the basic properties of neutralizing an acid with a base to reach such a point.

The group’s project is strictly the process design of the split stream leaching—all equipment will be developed later. The process must be designed and tested to meet the standards for Class A sludge, which requires that certain pollutants and chemicals be kept at or below a certain level. In order to meet these standards, the optimal amount of acid and base to be mixed with varying sludge samples was tested. The pH after the treated sludge streams are re-combined must also fall within the government specifications.

“This [method] is something that should definitely be considered for regular use at a municipal waste treatment center,” says Bajek. “The sludge that our technique makes can be used as a fertilizer, so the centers will not only save money on the actual method of making Class A sludge, but they can also profit from selling the sludge.”

Currently, the split stream process does not exist for mainstream use, but Dr. David Vaccari, the group’s academic director and department director for Environmental and Ocean Engineering, has a patent disclosure on the idea.

With 6.5 million tons of dry solids produced annually in the United States alone, sludge serves as a hidden renewable source that can cut down on cost of both finite resources and synthetic fertilizers. A process like split stream leaching will create the means to utilize such a product without the expense that comes with current treatment methods.