A hybrid MBBR system with intermediate ozonation: a solution for advanced car wash wastewater treatment

ABSTRACT

Flowchart and graphs showing carwash wastewater treatment via MBBR and ozonation: over 80percent DOC elimination in Zahn-Wellens test, tilde60–62percent total carbon removal by MBBR, and an extra tilde5percent removal with biofilm inhibition via ozonation.

Climate change makes wastewater treatment increasingly important. Germany's car wash facilities consume 50–250 L of drinking water per car, summing up to ∼50 million m3 annually. Improved treatment, particularly biological processing, would significantly reduce this consumption, as more process water could then be reused. A lab-scale hybrid moving bed biofilm reactor (MBBR) was treated with synthetic car wash wastewater. Following an initial MBBR stage and a subsequent sedimentation tank, the flow was split into parallel treatment lines. In the test line, the wastewater was ozonated and subsequently treated in a downstream MBBR. In the control line, the wastewater was aerated and then likewise treated in a separate second MBBR. The Zahn-Wellens test showed that the washing chemistry itself is inherently biodegradable. The MBBR unit achieved 57–61% removal of total carbon; combined biological stage plus ozonation reached ∼68–69%. This additional removal of up to 12% was statistically significant at the higher ozone dose; it was attributable not to enhanced bioavailability but to the oxidative effect of ozone, observed at ozone/total carbon ratios between 0.15 and 0.2, which corresponds to ozone/DOC ratios of 0.3–0.4. No toxicity of the processed water was detected in Pseudomonas growth inhibition tests using agar plates.