Start-up and maturation phases of a full-scale, high-rate anaerobic pond bioreactor^® plus improved facultative ponds to treat municipal wastewater

Results of the start-up and maturation phases of a full-scale, high-rate anaerobic pond bioreactor (HRAPB)^® plus improved facultative ponds (IFPs) to treat municipal wastewater are presented (COD_t: 759 mg L⁻¹, COD_f: 219 mg L⁻¹, S-SO₄^2–: 102 mg L⁻¹, and Cr⁺: 1,500 μgL⁻¹). The start-up of the HRAPB^® comprised, first, the application of a selective pressure increasing up-flow velocity rates. Second, batch stages between successive rates were allowed until 70% of the initial COD_f was removed. The IFPs were left in batch and ended when in-pond Chlorophyll-a concentration reached 800 μgL⁻¹. Subsequently, the system underwent gradual maturation and reached effluent concentrations of COD_t: 223 mg L⁻¹, COD_f: 50 mg L⁻¹, and Cr⁺: 60 μgL⁻¹. The actual efficiency of the system compared with the expected design efficiency was lower given the characteristics of the influent wastewater biochemical oxygen demand/chemical oxygen demand ratios < 0.4, presence of Cr⁺ >1,000 μgL⁻¹, and variations in both conductivity (500–4,500 μScm⁻¹) and pH (6.5–10.5 units). Nonetheless, the system exhibited an adaptation state in less than 1.5 months and yielded an ST/SV ratio of 0.46, and specific methanogenic activity of 0.43 g-CH₄-CODg⁻¹SV⁻¹d⁻¹ for HRAPB^®; the in-pond Chlorophyll-a was on average 1,200 μgL⁻¹ in the IFPs_, which demonstrated the robustness of these eco-technologies in tropical conditions.