Toilet paper and food waste in UASB reactors: A contribution to reducing the amount of conventional solid waste disposal

Abstract

The release of toilet paper (TP) and food waste (FW) in domestic sewage is a common practice in developed countries. Nevertheless, this practice has started to be used in developing countries where anaerobic digestion is applied. Therefore, this work aimed at evaluating the influence of the presence of TP and FW on the anaerobic digestion process in UASB reactors. During the experiment, two UASB reactors (8L) were fed with synthetic domestic sewage with the addition of toilet paper (TPR) and food waste (FWR) residues, respectively. In the first stage of the experiment (S‐I), the reactors operated with an organic load of 0.97 kg COD.m–3.d–1 (TPR) and 0.96 kgCOD.m–3.d–1 (FWR) and, in the second stage (S‐II), the quantities were increased to 1.58 kgCOD.m–3.d–1 (TPR) and 1.35 kgCOD.m–3.d–1 (FWR). In the experimental period of 110 days, the parameters total and filtered COD, series of solids, pH, alkalinity, and VFA were monitored. The mean removal of total COD was of 79±1% (S‐I) and 75±1% (S‐II) for TPR, and of 81±2% (S‐I) and 76±1% (S‐II) for FWR. Regarding VSS, the mean removal was of 94 ± 2% (S‐I) and 97 ± 1% (S‐II) for TPR, and of 95 ± 3% (S‐I) and 96 ± 1% (S‐II) for FWR. The VFA/TA ratio increased from S‐I (0.03 for TPR and FWR) to S‐II (0.17 to TPR and 0.10 to FWR), responding to the organic load increases, but still in the range of process stability. The added toilet paper or food waste were efficiently removed in both stages, reaching removals higher than 75%. In general, both reactors presented a good performance for the anaerobic process even under changes in organic load and influent composition. This experiment showed the feasibility of the combined treatment of TP or FW with domestic sewage in UASB reactors.