This review aimed to analyse the current state of management practices for poultry manure in Poland and present future perspectives in terms of technologies allowing closing the loops for circular economy, and thus recovery of nutrients and energy. The scope of the review focused primarily on: (1) the analysis of poultry production and generation of poultry manure with special references to quantities, properties (e.g. fertilizing properties), seasonality, etc.; (2) the overview of current practices and methods for managing poultry manure including advantages and limitations; (3) the analysis of potential and realistic threats and risk related to managing poultry manure, and also (4) the analysis of promising technologies for converting poultry manure into added value products and energy. The review addressed the following technologies: composting of poultry manure to obtain fertilizers and soil improvers, anaerobic digestion of poultry manure for energy recovery, and also pyrolysis of poultry manure into different types of biochar that can be applied in agriculture, horticulture and industry. Poultry manure is rich in macro- and micronutrients but also can contain various contaminants such as antibiotics or pesticides, and thus posing a realistic threat to soil and living organisms when applied to soil directly or after biological treatment. The main challenge in poultry manure processing is to assure sufficient closing of carbon, nitrogen and phosphorous loops and safe application to soil.

Poultry manure (PM) has become a serious environmental problem due to large scale of industrial production and unsustainable management, causing emissions of greenhouse gases (GHGs), odors, leakage of nutrients as well as inorganic, organic and biological pollutants. The main goal of this review was to get a better understanding of carbon, nitrogen, and phosphorous cycles in processing of poultry manure with the most common technologies such as composting, anaerobic digestion, or thermal processes, e.g. pyrolysis. The carbon contained in organic matter (ca. 31%) is mineralized and humified under aerobic conditions (matter recovery) and/or converted into biogas under anaerobic conditions (energy recovery). PM as a feedstock for pyrolysis to obtain biochar may effectively store and prevent C, thus contributing to climate change abatement. During composting, nitrogen is reduced from the compost mixture by leachates in the form of NH₄⁺, NO₃⁻ or gaseous emissions of NH₃, N₂O, N₂. The C/N ratio is also decisive parameter. Most environmental threats of unmanaged PM result from ammonia and nitrous oxide emissions, being higher for PM compared to cattle and cow manure independently of technological processes. The phosphorous in PM is mainly inorganic (32-84%). Using untreated manure as a fertilizer does not allow taking up high doses of phosphorus contained in poultry manure, so the excess accumulates in the soil and then leaches into groundwater. Biochar and struvite are an alternative to storage and source of high concentrations of phosphorous. Cycles of carbon, nitrogen and phosphorus are an integral effect of technologies used for PM management. Graphical Abstract

Sewage sludge, in particular from the food industry, is characterized by fertilizing properties, due to the high content of organic matter and nutrients. The application of sewage sludge causes an improvement of soil parameters as well as increase in cation exchange capacity, and thus stronger binding of cations in the soil environment, which involves the immobilization of nutrients and greater resistance to contamination. In a field experiment sewage sludge has been used as an additive to the soil supporting the phytoremediation process of land contaminated with heavy metals (Cd, Zn, and Pb) using trees species: Scots pine (Pinus silvestris L.), Norway spruce (Picea abies L.), and oak (Quercus robur L.). The aim of the research was to determine how the application of sewage sludge into the soil surface improves the phytoremediation process. The conducted field experiment demonstrated that selected trees like Scots pine and Norway spruce, because of its excellent adaptability, can be used in the remediation of soil. Oak should not be used in the phytoremediation process of soils contaminated with high concentrations of trace elements in the soil, because a significant amount of heavy metals was accumulated in the leaves of oak causing a risk of recontamination.