CAP Holding SpA

Financed by: CAP Holding SpA Period: 2016-2017

Introduction

The CAP Holding sewage treatment plant (Bresso / Niguarda, Milan) is based on activated sludge technology and is equipped with anaerobic digestion plants for the production of biogas from this material. A validation unit for the upgrading of biogas to biomethane was installed on the plant, built and managed by ECOSPRAY Technologies Srl The final objective of the trials therefore consists in the evaluation, for the first time in the Italian national territory, of the technical feasibility and environmental sustainability of biomethane production from sewage sludge.

Description

On a weekly basis, biomethane samples were taken in triplicate, for the subsequent determination of the following parameters: methane; carbon dioxide; hydrogen; hydrogen sulfide; oxygen. The higher calorific value, the density and the Wobbe index were also determined. The samplings were carried out by the CAP staff following a training carried out by the CNR staff. These measures made it possible to verify the technical and regulatory possibility of using biomethane as a fuel for transport. At the beginning and at the end of the testing period, the following parameters were also determined: total sulfur; total fluorine; total chlorine; mercury. Furthermore, again at the beginning and end of the testing period, the volatile organic compounds present in the biomethane were sampled and analyzed, for subsequent identification and quantification by gas chromatography / mass spectrometry. The same analyzes described were carried out on the incoming biogas, in order to assess the efficiency of clean up and upgrading. The characterization of the secondary components present in the incoming biogas and the outgoing biomethane made it possible to appreciate any insubstantial differences in the composition of the biomethane produced through the specific biomass (sewage sludge) compared to biomethane from agro-zootechnical residues. The study of these insubstantial differences (which are not an immediate impediment to the use of biofuel for the intended purposes) allows to identify the optimal protocol for purification and use of biomethane, and to favor its subsequent diffusion in other sectors. Furthermore, in order to evaluate the efficiency of the process and the environmental impact, the composition of the off-gas was analyzed, that is the gaseous effluent produced together with the biomethane, enriched in carbon dioxide. The off-gas analysis protocol is the same applied to biomethane: methane, carbon dioxide, hydrogen, hydrogen sulphide and oxygen quantified on samples in triplicate on a weekly basis; volatile organic compounds, total sulfur, total fluorine, total chlorine and mercury at the beginning and end of the testing period.

Aims

The activity aims to evaluate the effectiveness of a prototype for the upgrading of biogas to biomethane at a sewage sludge treatment plant. The purpose of the monitoring is to assess the quality of the biomethane produced for subsequent use as a fuel for transport. Another objective of the activity is to verify that the performance of the prototype remains constant for the entire testing period.