Coupled microalgal–bacterial biofilm for enhanced wastewater treatment without energy investment

In view of water-resource depletion, treated wastewater can serve as an alternative source for crop irrigation. However, conventional wastewater-treatment plants are energy-intensive and costly to construct and operate, especially for lower middle-income countries. The present study focused on improving the quality of wastewater by incorporating a coupled microalgal–bacterial biofilm (CMBB) treatment in wastewater ponds. Standard polyether sponges were dipped in raw wastewater samples to enhance biofilm development on them. The enriched sponges were used to treat wastewater, with or without external energy for aeration. Wastewater parameters were analyzed during the enrichment and treatment processes. The CMBB technology and aeration resulted in similar improvement of effluent quality, but the former saved on energy costs, and reduced total chemical oxygen demand (COD) by 36 % within 24 h and 71 % within 4 days; the values of biochemical oxygen demand (BOD), ammonium and phosphates decreased by 80 %, 64 % and 95 %, respectively, within 7 days. The resultant COD and BOD values were below the maximum allowed for reuse and discharge.