The impact of tourism seasonality on the Design and operational management of a bioreactor system for biowaste treatment: A case study of istria county

Biowaste accounts for a significant share of total biodegradable waste in the Republic of Croatia. In regions with developed tourism, such as Istria County, which records over 26
million overnight stays per year, waste treatment systems must be designed to withstand extreme seasonal fluctuations. The aim of this work is to analyse the dynamics of biowaste generation and define optimal operating parameters for the bioreactor to achieve process stability.
The analysis uses data from 2019, assuming that about 55% of total kitchen biowaste generated by households is collected for processing. An estimated annual volume of 9,519
tonnes, including food and green waste, was processed at a fixed density of 0.609 t/m³. A bioreactor system (7.0 × 3.5 × 3.5 m) was designed with the key criterion that the filling time of an individual unit should be between 1 and 2 days.
The research identified pronounced seasonality, with volumes ranging from 547 t/month in January to 947 t/month in July. To cover the peak summer load, a capacity of 19 bioreactors is required which, with a filling height of 2.50 m, ensures a filling time of 1.4 days per unit. Off-season operating options were analysed, including running all 19 bioreactors at a lower filling height and intensive use of 14 bioreactors while maintaining the standard filling height.
The strategy of intensive use of 14 bioreactors in the off-season (with a filling time of 1.3 days) proved more effective for maintaining stable biological processes. The remaining five bioreactors are recommended as operational reserve or for regular system maintenance. This management model enables high flexibility and efficiency of the system despite
variations in incoming waste volumes.