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Landspreading of sewage sludge remains the most economical and practical means for its disposal, with some countries, such as Ireland, disposing up to 90% to land. Its nitrogen, phosphorus and metal content make it an effective fertiliser replacement. However, there are potentially serious issues associated with its use in agriculture. These range from impacts on the environment through surface losses of nutrients, metals, pharmaceuticals and personal care products (PPCPs), and emerging contaminants, as well as build-up of contaminants in the soil and transfer to the human food chain. This paper details the main findings of an Irish Environmental Protection Agency (EPA)-funded study which investigated these issues. This study characterised treated sewage sludge ( biosolids ) from wastewater treatment plants employing different means of sludge treatment, examined surface losses of various physico-chemical parameters following land application, measured metal uptake by ryegrass, and modelled the potential impacts on human health. This study was funded by the Irish EPA (Project reference number 2012-EH-MS-13). non-peer-reviewed

In Ireland, agricultural activities have been identified as major sources of nutrient input to receiving waters and it has been estimated that these activities contribute 75.3% of the nitrogen (N) and 33.4% of the phosphorus (P) in these waters. Strategy at European level focuses on the prevention of nutrient loss by improved farm management. However, it does not focus on nutrient remediation or incidental nutrient loss of farmyard manures to surface and groundwater. This review describes the impact of agriculture on the environment in Ireland and examines emerging technologies for agricultural wastewater treatment. An integrated approach at pre-treatment and field stages for nitrate (NO3) remediation and P control is recommended. peer-reviewed

Globally, agriculture urgently needs alternative sources of phosphorus (P). Presently, global agriculture is over-reliant on inorganic mineral P fertilisers sourced from finite mining sources. This is especially relevant in the European Union (EU), since Europe lacks natural rock phosphate deposits. There are many alternative organic sources of P, which could be used at low cost in agriculture to grow crops. For example, as one of the largest agricultural-food sectors in EU, the dairy processing industry generates large amounts of P-rich dairy processing sludge (DPS), which can be further processed into secondary-raw-material-based fertilising products, referred to as STRUBIAS (STRUvite, BIochar, or incineration AShes). As DPS and DPS-derived STRUBIAS products have the potential to be used as bio-based fertilisers, to encourage farmers to choose such fertiliser alternatives and stimulate their access to the market, the EU has implemented changes to the Fertiliser Regulations. To date, few studies have focused on the potential of these products to be used as agricultural fertilisers, which has hindered their incorporation in agricultural nutrient management planning. This thesis aims to address the knowledge gaps associated with their agronomic performance and potential environmental risks when reused as fertilisers in agriculture. Specifically, the aims of this thesis were to: (1) quantify the nutrient and metal content of a range of DPS and DPS-derived products (2) compile a database and develop a MS ExcelTM calculator programme to provide farmers with a quick and safe way to reuse these products (3) determine the mineral fertiliser equivalent value (MFE) of a range of these products when used to grow ryegrass and spring wheat, and (4) examine how the different application rate (optimal versus high) and calculation methods (with and without chemical fertiliser response curves) affect MFE results, which, in turn, will enable a standard approach to be used in fertilisation. 2025-03-09

Dairy farms produce dairy soiled water (DSW) during the milking process, which consists of a mixture of water, cow faeces, urine, milk, detergents, and sediment. Land spreading is the most common disposal method for DSW. However, when applied at rates that exceed the nutrient demand of the herbage, or when applied under unfavourable soil and weather conditions, land application of DSW can result in pollutant loss to associate receiving water bodies (ground and surface waters). Constructed wetlands (CWs) and intermittently loaded sand filters (ISFs) have been investigated for the treatment of agricultural wastewaters, and have been shown to provide efficient and sustainable treatment of DSW. Nevertheless, the large surface area requirements for treatment, poor long term phosphorus (P) removal, and media clogging, are the main limitations of these systems. The addition of chemical coagulants to DSW, such as aluminium and ferric salts, have been found to be effective in clarifying DSW and removing organic matter (OM), suspended solids (SS), P, and pathogens. Such chemicals are already being used on Irish farms. For example they have been shown to be effective at reducing gaseous emissions during storage of slurry and DSW and indeed preventing P losses in runoff from subsequent land application of these wastes to fields. To date, a combination of a coagulation process and CWs or ISFs have not been used to treat DSW. The present research introduces a novel coagulation step before wastewater is treated by CWs or ISFs. The hypothesis of this thesis is that the addition of a coagulation process as a pre-treatment step could improve the performance of CWs and ISFs, and overcome the shortcomings of the individual capacities of these systems. In addition, this step would negate the need for CWs to expand in size as their P remediation capacity would be maintained at a high level. This is likely to increase the uptake of such systems on farms in the future. Therefore, the objective of this thesis was to investigate the combined capacities of coagulation-CWs and coagulation-ISFs and compare the results to the individual capacities of conventional CWs and ISFs. To achieve this objective, an optimum chemical coagulant, mixing time and dosage was identified in improving effluent quality of DSW. Following this, replicated pilot-scale hybrid CWs and ISFs, each employing a preliminary coagulation process using ferric chloride (FeCl3), were operated for a 43-wk period on a dairy farm (representing an entire milking season in Ireland). Conventionally designed CWs and ISFs were used as study controls. The hybrid systems performed better and were able to operate effectively at higher hydraulic loading rates than conventional CWs and ISFs. The performance of the hybrid systems exceeded that of the conventional systems, obtained removal efficiencies ≥ 99% for all measured water quality parameters (chemical oxygen demand, SS, P, nitrogen and turbidity), and complied with EU directives concerning urban wastewater treatment. The effluent quality from the conventional ISFs deteriorated over the timeframe of the study until clogging occurred, while the hybrid ISFs continued to perform effectively without any evidence of clogging or P breakthrough. Examination of the filter media in both filter types showed that conventional ISFs retained more biomass than hybrid coagulation-ISFs. Conventional ISFs lost approximately 85% of their initial infiltration capacity in the uppermost layer due to biomass build-up versus 40% loss for hybrid ISFs. Overall, hybrid coagulation-CW/ISFs are a promising technology that require a small area (75% reduction in footprint in comparison to conventional systems) and minimal maintenance, and produce excellent effluent quality. The final effluent from the hybrid system may be legally discharged to receiving waters, or recycled to wash farm yards, protecting water quality and saving water, respectively. In parallel, the sludge portion generated from the coagulation process, can be applied to land as a bio-based fertilizer without adverse impacts on the grass growth, and with the added benefit that there would be a substantially lower risk of nutrient losses from such a fertilizer to waters. This management approach could eliminate or reduce the pollution risk along surface pathways to waters, and minimise the overall net cost compared to land application of raw DSW (without treatment). Future research should focus on the life cycle and circularity assessment of these hybrid systems.