Case study: Treating sugary wastewater

A confectionery company faced challenges with a sugary wastewater stream from process wastewater with an extremely high sugar content. It used Aquacycl’s BETT system to treat the wastewater onsite and remove up to 95% of organics.

The “sugarwater” challenge

Sugar processing is one of the most water-intensive industries. The wastewater from sugar refining and processing contains high brix (which translates to high chemical oxygen demand or COD), total suspended and dissolved solids (TSS and TDS), color, low pH and odor. The composition of the effluent makes it difficult to treat or discharge.

The confectionery company faced challenges with a specific waste stream from process wastewater with an extremely high sugar content. This specific waste stream (“sugarwater”) requires pretreatment or dilution prior to land-application; and cannot discharge to the onsite aerobic treatment facility due to carbon toxicity issues that would occur.

Solving the sugary wastewater challenge

Until now, attempts to commercialize a technology that can treat this waste stream have failed due to high material and production costs, scalability challenges and efficiency losses that minimize energy recovery during the treatment process. Aquacycl is the first company to solve the technical challenges that have previously limited the commercial use of microbial fuel cell technology.

Aquacycl installed a fully automated and containerized 12-reactor demonstration unit (BETT Demo Unit) to continuously treat 160 gpd (727 liters/day) of the sugarwater and enable a clear understanding and cost model for how BETT systems could be applied at full-scale for sugar industry wastewater treatment. System COD removal and power production were monitored during the demonstration. The inflow sugarwater COD ranged from 100,000-300,000 mg/L under continuous flow conditions. Batch operations were also required corresponding to production shutdowns associated with holidays and other facility operations.

The results

The BETT Demo Unit demonstrated its applicability and efficiency in treating high-strength sugary wastewater. The BETT Demo Unit accomplished an average 10% COD removal (18,377 mg/L) in a 4-hour hydraulic residence time with only 12 BETT reactors in hydraulic series (Figure 2). The COD removal capacity of the system ranged from 2,200 mg/L to 50,000 mg/L. Lower removal rates were observed when reestablishing continuous mode after planned facility shutdowns. The system only requires 24-48 hour recovery period to reach normal performance metrics after a system shut-down or batch operation. These results showcase how microbial fuel cells can be used for treatment of high-organic wastewaters. Further, the system scales modularly. By adding more reactors in a treatment train, and operating multiple treatment trains, the BETT reactors can be used to remove up to 95% of organics with flows between 2,500 gpd to 10,000 gpd.

One benefit of Aquacycl BETT system is the limited biomass production. During sugarwater treatment the BETT Demo Unit only generated 0.03 to 2.5% biomass from the COD removed (Table 1). In comparison to other conventional technologies, this translates to negligible biomass production (Figure 3). The biomass generated from BETT ranged between 4 to 112 mg/L VSS compared to 381 to 4,615 mg/L VSS if the wastewater was anaerobically treated; and 1,522 to 18,462 mg/L VSS for aerobic processes (assuming identical COD loading in all cases).

The net energy recovery (NER) from BETT was up to 1.6 kWh/ kg-COD removed comparable to anaerobic digestors combined with methane conversion to electricity. The electricity was generated as direct DC power, with no intermediate methane production.

Aquacycl

www.aquacycl.com