Abstract:In the Mediterranean region, the disposal of residues of olive oil industries represents an important environmental issue. In recent years, many techniques were proposed to improve the characteristics of these wastes with the aim to use them for methane generation in anaerobic digestion processes. Nevertheless, these techniques, in many cases, result costly as well as difficult to perform. In the present work, a simple and useful process that exploits H 2 O 2 in conjunction with lime is developed to enhance the anaerobic biodegradability of wet olive mill wastes (WMOW). Several tests were performed to investigate the influence of lime amount and H 2 O 2 addition modality. The treatment efficiency was positively affected by the increase of lime dosage and by the sequential addition of hydrogen peroxide. The developed process allows reaching phenols abatements up to 80% and volatile fatty acids productions up to 90% by using H 2 O 2 and Ca(OH) 2 amounts of 0.05 gH 2 O 2 /gCOD and 35 g/L, respectively. The results of many batch anaerobic digestion tests, carried out by means of laboratory equipment, proved that the biogas production from fresh wet olive mill wastes is hardly achievable. On the contrary, organic matter abatements, around to 78%, and great methane yields, up to 0.34-0.35 L CH4 /g CODremoved , were obtained on pretreated wastes.

a b s t r a c tOlive mill residues, due to their low biodegradability and high amounts of phytotoxic compounds, are difficult to treat by means of conventional biological processes. In recent years several pretreatments of these by-products have been developed to increase their anaerobic biodegradability and to exploit them for biogas production. However, these processes are often expensive and hard to carry out. In this paper an effective and easy-to-manage pretreatment, based on the use of hydrogen peroxide under alkaline conditions without the addition of catalysts, is proposed. Many experiments were carried out on wet olive mill wastes in order to evaluate the influence of pH and peroxide dosage on process performance. Polyphenols abatements of about 72% were observed. The kinetic analysis of experimental results allowed us to investigate the reaction mechanisms and to optimize the operating procedures. This permitted to reduce the peroxide dosage without the occurrence of a remarkable performance reduction. By means of batch digestion tests, conducted in a pilot scale plant without co-substrates addition, it was verified a negligible biogas production detectable on raw olive mill waste, while a COD reduction about of 77% and a high methane yield of approximately 0.328 L CH4 /gCOD removed were obtained on pretreated waste.

Abstract:The treatment of landfill leachate, due to its great polluting load, is a very difficult task. In particular, the abatement of high ammonium concentrations represents one of the main issues. Among the available techniques, struvite precipitation is an effective method for the removal and recovery of NH 4 + load. However, due to the lack of phosphorus and magnesium amounts, the struvite formation results in an expensive process in the leachate treatment. To overcome this issue, in the present work, we developed a simple and suitable method for ammonium removal by the multiple recycling of struvite decomposition residues. In this regard, a procedure for acid dissolution of struvite, produced by using industrial grade reagents, was initially defined. The effect of pH, temperature, and acid type was investigated. The experimental results proved the effectiveness of both hydrochloric and acetic acid, which allow a high and selective release of ammonium at T = 50 • C and pH = 5.5. The multiple reuse of decomposition products, combined with the supplementation of a small quantity of phosphorus and magnesium at molar ratios of n(N):n(Mg):n(P) = 1:0.05:0.05, guarantees stable NH 4 + abatement of about 82%. The proposed process allows a cost saving of around to 74% and can be easily applied in industrial treatment plants.

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