LIVESTOCK MANURE TREATMENT FOR NUTRIENTS REMOVAL: CONSOLIDATED TECHNIQUES, EMERGING PROBLEMS AND NEW APPROACHES

Intensive farming practices and their continuous spread generate a large amount of livestock manure that cannot be disposed properly. This can cause water, air and soil contamination. Therefore, the identification of strategies for correct management of livestock manure is necessary for limiting environmental pollution. Nitrification/denitrification process (NDN) represents one of the most applied solutions. However, at real scale, many of those facilities that adopt this process suffer from managing issues and malfunctioning. Recently, alternative techniques have been applied to the recovery of nutrients along with their removal. An example is solid/liquid separation using chemicals to remove phosphorus and concentrate it into solid fraction, easier to handle. Other concerns are ammonia and greenhouse gases emissions derived from the management and the treatment of livestock manure. Their assessment is the first step to identify and apply proper mitigation strategies focused on limiting emissions. In this thesis, the application of biological processes for the removal of nitrogen from livestock manure was investigated to find possible improvements. First, a review of the state of the art of nitrification/denitrification process applied in the sequencing batch reactor system (SBR) to livestock manure was carried out to produce an overview on the SBR technology, monitoring parameters and process optimization. This can help the identification of SBR strengths and weaknesses when these systems are adopted for the livestock manure treatment and can support the definition of the best operation settings to adopt for reaching desired removal rates. Several treatment plants were monitored to attest operational and removal efficiencies achieved. The aim of these monitoring campaigns was the identification of possible improvements for NDN (nitrification/denitrification) plants. Eventually, the application of the NDN process in laboratory SBR systems was analysed to study how the nitrogen removal rate changes with the variation of the slurry inlet characteristics and of the applied operational settings. Concerning emissions, the use of different types of dynamic hoods and static chamber for estimating GHGs and NH3 emissions derived from livestock manure was investigated. Regarding recovery of phosphorus (P), the dissertation dealt with the evaluation of the effect of two additives (calcium hydroxide Ca(OH)2 and aluminium sulfate Al2(SO4)3) on the solid/liquid separation process of P, Copper and Zinc from raw slurry and co-digested slurry before and after a physico-chemical ammonia stripping treatment. The results outlined that the performance of monitored SBR treatment plants at real scale are less than expected. Rarely TAN removal exceeds 50% even if at lab-scale observed removal rates were higher (up to 95%). Pre-treatments are necessary to improve performance of treatment plants. Moreover, the upgrading of proper process control system and its correct use are required. These should be considered also if a new SBR is designed. Ammonia and GHGs emissions occur during the entire livestock manure management chain and their evaluation is possible applying the direct method. In particular, dynamic hoods can be useful tool for measuring site-specific NH3 and GHGs emissions except for CH4. The application of solid/liquid separation process for phosphorus removal using aluminium sulphate allowed to reach removal rates higher than 70%. This additive enhanced also the removal of suspended solids (58%), copper (up to 94%) and zinc (up to 93%).