Toxicity assessment of sanitary landfill leachate before and after Fenton treatment process.

Sanitary landfills are widely accepted and promoted as the environmentally friendly way to properly dispose of solid waste. However, a harmful aspect is the leachate generation and management, which are currently recognized as one of the greatest challenges in the environmental engineering field. Due to the high leachate recalcitrance, Fenton treatment has been accepted as a viable and efficient treatment process, which significantly reduces the organic matter: 91 % of COD; 72 % of BOD5; and 74 % of DOC. However, the acute toxicity of leachate must be assessed, mainly after the Fenton process, with the view of performing a low-cost biological post-treatment of the effluent. Despite the high redox potential, degrading 185 organic chemicals compounds identified in raw leachate, the present work reports a removal efficiency of almost 84 %, counting 156 organic compounds removed, and almost 16 % of persistent compounds. After Fenton treatment, 109 organic compounds were identified, beyond the persistent fraction of almost 27 %, wherein 29 organic compounds remained unchanged after Fenton treatment, counting 80 new short chain and lower complexity organic compounds formed. Despite the biogas production ratio increase (3-6 times), and significant enhancement of the biodegradable fraction susceptible to oxidation in respirometric test, a higher reduction in the oxygen uptake rate (OUR) was identified after Fenton treatment due to persistent compounds and their bioaccumulation. Additionally, the D. magna bioindicator parameter indicated that treated leachate is three times more toxic than raw leachate.

Alkaline and acid solubilisation of waste activated sludge.

The influence of acidic and alkaline conditions on the solubilisation process of waste activated sludge (WAS) was investigated using HCl and NaOH at pH 2, 10, 11 and 12. The rise in concentration of solubilised compounds, the influence of reaction time, and the influence of the concentration of total solids (TS) during the solubilisation process were determined. Physical and chemical tests demonstrated that pre-treatment provided a release of compounds from the sludge floc matrix into the soluble fraction, characterising the solubilisation process. The highest degree of WAS solubilisation was observed when a pH of 12 was applied. Although largest effects were already attained after 0.25 h, WAS solubilisation continued reaching an increase in total dissolved solids by a factor 10.4 after 720 hrs. Under these conditions, the dissolved organic carbon (DOC), proteins, and carbohydrates resulted in releases up to 15, 40 and 41 times, respectively; phosphorus increased 5.7 times. Results indicate that by applying alkaline pre-treatment, higher TS concentrations can be treated per reactor volume compared to non-pre-treated WAS. Aerobic and anaerobic biodegradability tests showed increased bioconversion potentials in full-scale treatment plants. The respirometry tests ratify the improvement in solubilisation, with O2 consumption rates increasing 1.4 times, concomitant with an additional 261 mg·L-1 of the COD used, which represents 90% bioconversion of waste activated sludge. Biomethanisation test indicated an increase of 3.6 times relative to the blank.