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 (CODt: 759 mg L−1, CODf: 219 mg L−1, S-SO42–: 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 CODf 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 CODt: 223 mg L−1, CODf: 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.

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