Nature Sciences Department, New Bulgarian University, 21 Montevideo, 1618 Sofia, Bulgaria
Abstract. The present paper aims to assess nitrogen circulation in an eco-technical system for egg production. The experiments were conducted in modelled conditions in an anthropogenic ecosystem of the “mesocosm” type, in which the unit of the bio-consumers and three eco-technological chains modelling the unit of the bio-decomposers are modelled: manure storing for decontamination /a recommendation on good farming practices/, composting and anaerobic decomposition in an installation for biogas production. A new criterion was implemented for the assessment of the chemical heterogeneity in the biogenic nitrogen cycle in the modified trophic chain – retention coefficient /k/, which is defined as the ratio of nitrogen introduced into the system / nitrogen content in the feed: its quantity in the secondary biological production x 100. The chemical heterogeneity at the level of organisms /differences in the individual components of eggs/ and at the biocenotic level is established. The biogenic nitrogen cycle in the eco-technical chain for egg production is characterized by an uneven distribution in both products of the outflow. The largest amount of nitrogen is found in the egg whites (k = 0.45), while it decreases significantly in egg yolks (k = 0.17) and reaches k = 0.03 in the egg shell, a.k.a. heterogeneity on the level of organisms is established. The nitrogen compounds introduced through the feed ration are concentrated in manure (k = 25.33). Losses of nitrogen are established in two of the manure utilization technologies. The quantity of /k/ in the compost is 20.32, a.k.a. the loss of nitrogen compounds is 19.8%. The biggest losses are found in manure storage; according to the recommendations on good farming practices (k = 18.82) or the reduction of nitrogen is 25.7% compared with fresh manure. Due to redistribution of the chemical elements /a significant part of C, H and O are included in biogas/, there is nitrogen concentration in bio slime – k = 35.85 or 41.5% more than in fresh manure. When separated nitrogen is concentrated in the liquid fraction (k = 31.19), while in the solid phase k = 4.67 is established.