PROJECT DESCRIPTION
BACKGROUND
People living in industrial tannery districts, especially those close to wastewater treatment plants, have traditionally experienced poor air quality and odour problems caused by emissions of hydrogen sulphide (H2S) and other sulphurous compounds. The Santa Croce sull’Arno tannery district in Tuscany produces more than 80% of all Italian footwear and leather goods. The tannery district currently requires very large amounts of chemicals and energy to control sulphide emissions and odours. The industrial wastewater is characterised by a very high organic load (COD > 15 000 mg/l), typically with large amounts of natural and synthetic tannins. An innovative technology with high performance in the removal of pollutants from liquid and gaseous streams would improve the sustainability of the overall tannery district and, at the same time, help to meet Italian legal limits.
OBJECTIVES
The BIOSUR project aimed to demonstrate the economic feasibility, environmental sustainability, and technical applicability of an innovative technology for the removal of hydrogen sulphide from gaseous streams. The project planned to demonstrate the technology through the design, set up and operation of a pre-industrial scale prototype of a bio-trickling filter, which will be applied to real gaseous streams in a large tannery consortium’s wastewater treatment plant (WWTP). Specific objectives were to identify opportunities for the dissemination of promising innovative technologies; to contribute to reducing EU greenhouse gas emissions by 2020; and to involve public administrations in the dissemination of innovative technologies, in one of Europe’s biggest tannery districts covering some 400 tanneries.
RESULTS
The BIOSUR project demonstrated the environmental sustainability, technical applicability and financial feasibility of an innovative technology for the removal of hydrogen sulphide (H2S) from gaseous streams in a wastewater treatment plant (WWTP). Italprogetti, in collaboration with the University of Florence (Unifi), designed, constructed and installed the demonstration prototype with a new type of bio-trickling filter, called the Moving Bed BioTrickling Filter (MBBTF), which was equipped with discs made of different types of support media for biofilm growth. The main novelty of this technology is the coupling of a bio-trickling filter with rotating supports, and the prototype is a rare example of a full-scale moving bed bio-reactor for gaseous streams treatment in Europe. The project optimised process solutions, operating conditions (e.g. temperature and pH) and reactor configuration for the biological removal of hydrogen sulphide, and applied the prototype to clean up different gaseous streams in the WWTP of the Cuoiodepur tannery consortium.
The process was extensively monitored and evaluated. The project achieved an average removal efficiency for hydrogen sulphide of more than 80% when compared to a traditional static filter treatment, with an elimination capacity of more than 150 g/h H2S/m3. The elimination capacity of the project’s MBBTF was about one order of magnitude higher than the conventional elimination capacity for traditional static bed bio-trickling filters. This resulted in savings in the consumption of chemicals (mainly sodium hydroxide), which can be also completely eliminated, and in the consumption of energy by at least 30% with respect to a traditional chemical scrubbing process. Removal efficiency was found to be dependent upon H2S concentration peaks which, in turn, depend on the composition of the effluent to be treated.
The operating cost of the new biological process (as low as 1-4 €/Kg of H2S removed) is lower than that for traditional chemical scrubbing (7-20 €/Kg of H2S removed). This is mainly due to costs linked to energy and the consumption of chemicals. Consequently, the application of the technology would lower the carbon footprint of a conventional WWTP by about 1 200 tonnes of CO2 per year. The innovative moving bed bio-trickling filter will also in the long-term facilitate the control of biomass activity and removal, as the clogging of filters due to excessive biomass is a major problem for conventional bio-trickling filters. The project’s evaluation concluded that the technology offers a long-term sustainable application for the biological processing of concentrated gaseous streams at high volumetricloads.
The construction and fine tuning of the prototype were revealed to be more complex than originally planned, requiring the involvement of several experts and suppliers in parallel. The cost-effectiveness of applying the project’s technology could be increased if two main conditions are present: the potential receiving company already owns the WWTP required for the system to operate, and their technicians already hold basic knowledge on the biological production processes.
The project partners ensured that the demonstration system could be easily exploitable on a large scale, with technical details set out in a series of project reports. The technology is potentially of interest to companies operating in similar sectors obliged to reach targets set by the Waste Framework Directive (WFD) and other EU legislation. The project started a process of analysing the potential world market for the new technology. The replication of the project’s technology would be especially useful in tannery districts that typically use chemical scrubbing for H2S removal. More specifically, the staff of Cuoiodepur and the Unifi are in contact with three tannery wastewater treatment plants in the districts of Arzignano (Vicenza, Italy), Igualada (Catalogna, Spain), and Leon (Guanajuato, Mexico). The technology could also be transferred to several other industrial processes (e.g. paper making, oil and gas industry, pharmaceuticals, food processing, livestock farming) where hydrogen sulphide is present in wastewater.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).
An ex-post visit was carried out by the LIFE external monitoring team in November 2018. This confirmed the high relevance of the project to Italian and EU regulations relating to wastewater treatment and gaseous emissions from WWTPs. It concluded that the BIOSUR technology is an environmentally-sustainable method and a valid alternative to traditional chemical systems used to treat gaseous streams rich in hydrogen sulphide; with positive impacts in terms of energy, costs, environmental impacts and resource savings. The ex-post report noted that the project team demonstrated both the technical feasibility and the economic viability of the technology. The final configuration of the prototype showed how the new biological process can help to remove up to 230 g/m3h of hydrogen sulphide when operated in optimal conditions. This is about one order of magnitude higher than the conventional elimination capacity of traditional static bed bio-trickling filters, and it also prevents clogging. Moreover, the use of chemicals, mainly sodium hydroxide (NaOH) and oxygen, can be completely avoided or reduced in comparison to traditional chemical scrubbing. In the three years since the project ended, it was estimated that the operation of the technology has provided savings amounting to 15% of NaOH, 10% of energy, 5% of water and 12% of operational costs, compared to the configuration without the BIOSUR technology. This post-LIFE operation has proved the efficacy of the system and shown that it can consistently reduce the carbon footprint of WWTP emissions treatment. The BIOSUR technology has continued to attract widespread interest from potential companies, mainly tanneries, bio-gas plants and the paper industry. The major barrier so far to the replication of the technology has been the initial investment costs, linked to the fact that the optimisation of the system is site specific and therefore requires a preliminary analysis to be made. In the case of the bio-gas sector, where the technology has good potential, the main challenge is to adapt it to the anaerobic conditions of bio-gas plants.
