Variabilidade espacial e temporal nas características químicas do composto de resíduos alimentares produzidos em escala comercial

Abstract

Organic waste account for more than half of the USW generated in Brazilian municipalities and the PNRS points out that its reutilization should be promoted. Composting proves to be an important technology for this purpose. This study aimed to evaluate, by means off a new sampling method, originated from Theory of Sampling (TOS) of Pierre Gy, the spatial and temporal variability on physical, chemical and microbiological properties of the compost produced in full-scale composting facility treating food waste and tree pruning. For this purpose, 36 batches of compost produced at the municipal composting facility of Belo Horizonte were monitored from October 2015 to January 2017. To understand the origin of the variability in compost properties, we also analyzed the chemical characteristics of the windrows at the beginning of the composting and the wastes used to set up the windrows. The proposed sampling method TOS method (sampling after changing the geometric shape of the windrow), was more efficient in reducing sampling errors than the sampling method described in NBR 10,007:2004 trier method (sampling in the original shape of the windrow), although the latter may also be considered suitable for compost sampling (120 days of the process), providing that some conditions be met prior to sampling. Temporal variability in the properties of tree pruning waste (water content and CO/N ratio) influences windrows preparation for composting. Meanwhile, the high heterogeneity in food waste may cause temporal variability in nutrient content of the compost and make it difficult to comply with legislation. The guarantees required for organic fertilizers by MAPA (IN SDA n° 7/2016 e n° 25/2009) were not met for the following variables: maximum E. coli count (~ 95 % of noncompliance), maximum water content (~ 50 % of non-compliance) and maximum CO/N ratio (~ 50 % of non-compliance). There was total compliance with required limits values for pH, CO and N. Brazilian regulation also establishes a minimum value for each chemical property of the organic fertilizer, among the batches produced over time (deficiency tolerance), which was not exceeded for pH and CO. Non-compliances with deficiency tolerance were up to 10 % for N content (dry matter), CTC, CTC/CO ratio and CO/N ratio, from 11 to 25 % for P content (dry matter), N content (natural matter) and water content and 26 50 % for K content (dry matter and natural matter) and P content (natural matter). Non-compliance to the deficiency tolerance for N, P e K contents (dry matter) can mainly be attributed to differences in the initial condition of the windrows (e.g. tree pruning proportion, nutrient content) and in the operational activities among windrows (frequencies of turning and water addition). Differences in the degree of organic matter degradation among the 36 windrows was possibly the main reason for non-compliance of CO/N, CTC and CTC/CO ratio