Recycling of Two-Phase Olive-Mill Cake “Alperujo” by Co-composting with Animal Manures

Abstract

The use of poultry manure or goat/sheep manure in the co-composting of the two-phase olive-mill cake "alperujo" (ALP) with olive leaf (OL) is compared by studying organic-matter mineralization and humification processes during composting and the characteristics of the end products. For this, two different piles (P1 and P2) were prepared using ALP with OL mixed with poultry manure (PM) and goat/sheep manure (GSM), respectively, and composted by the turned windrow composting system. Throughout the composting process, a number of parameters were monitored, such as temperature, pH, electrical conductivity (EC), organic matter (OM), OM losses, total organic carbon (C org ), total nitrogen (N t ), C org /N t ratio, and the germination index (GI). In both piles, the temperature exceeded 55 • C for more than 2 weeks, which ensured maximum pathogen reduction. Organic-matter losses followed a first-order kinetic equation in both piles. The final composts presented a stabilized OM and absence of phytotoxins, as observed in the evolution and final values of the C org /N t ratio (C org /N t < 20) and the germination index (GI > 50 percent). Therefore, composting can be considered as an efficient treatment to recycle this type of waste, obtaining composts with suitable properties that can be safely used in agriculture.

Chemical structures and characteristics of animal manures and composts during composting and assessment of maturity indices

“…The temperature evolution of three manure composts followed the same pattern as that of other reports [ 7 , 11 , 13 , 14 ]. The cattle and chicken manure composts reached the thermophilic temperature faster and had a shorter thermophilic phase than the swine manure composts did.…”

“…Several temperature peaks in swine manure composts could be due to its distinct chemical compositions and microbial communities. Compared with those in the studies with the addition of organic bulking agents [ 7 , 13 , 14 ], the peak temperatures of our three manure composts were much lower. This may be due to the enhanced temperatures from the faster degradation of organic matter due to appropriate C/N ratios adjusted by organic bulking agents.…”

“…However, Tiquia and Tam [ 13 ] reported increased C/N in poultry litter composts. The pH usually increased with composting [ 8 , 9 , 11 , 14 ], but Tiquia et al [ 1 ] found a decline pH trend during 91-day composting of pig litter. The decreased NH 4 + -N and increased NO 3 - -N often led to low NH 4 + -N/NO 3 - -N ratios at the end of composting [ 10 , 11 , 15 ].…”

“…The decreased NH 4 + -N and increased NO 3 - -N often led to low NH 4 + -N/NO 3 - -N ratios at the end of composting [ 10 , 11 , 15 ]. The composting temperature evolution can be generally divided into three distinct phases, mesophilic, thermophilic, and mesophilic/ maturation stages [ 7 , 11 , 13 , 14 ].…”

“…Germination index (GI) was frequently used to estimate phytotoxicity and thus maturity of composts, which is an important criterion for evaluating the suitability of composts for land application. Generally, GI increased during composting [ 7 , 14 , 16 , 17 ].…”