Integrating aeration and rotation processes to accelerate composting of agricultural residues

Abstract

The active phase of conventional static composting systems varies dramatically, ranging from several weeks to several months. Therefore, this study was to examine the effect of a combined continuous aeration-rotation process on shortening the active phase of composted material. A mixture of tomato plant residues with 20%-chicken manure ( v / v ) was composted in two identical pilot-scale bioreactors. One of them was static, and the other was continuously rotated at 3 rpm; each was supplied with continuous aeration. Compost temperatures ( T c ) were measured throughout the composting process; the moisture content ( MC ) and carbon/nitrogen ratio ( C/N ) were measured at the beginning and end of the experiment. The quality and stage of compost were evaluated at the end of the experiment using Dewar, Solvita, and visual tests. Continuous aeration-rotation significantly reduced the active phase period to 4.5 days, increased the compost temperature ( T c ) to 60°C after 3 days of operation, and remained at 50–65°C for approximately 3 consecutive days (thermophilic stage). In contrast, compost in the static bioreactor remained in the mesophilic stage ( T c < 45°C). During the composting process, the C/N ratio was reduced from 30/1 to 23/1 in the rotating bioreactor, while it remained at 30/1 in the static bioreactor, indicating that the nitrogen content was not a limiting factor affecting the composting process. The MC was within the optimum range for microorganisms (58–61%) for both bioreactors. After the active phase had ended in the rotating bioreactor, the compost was inactive and ready for further maturation, while compost from the static bioreactor was still immature and active. These results show that the proposed method can be done on a commercial scale to significantly reduce the composting period and to enhance the compost stability and productivity.

Toward Sustainability in Rural Areas: Composting Palm Tree Residues in Rotating Bioreactors

“…The fixed tube was used for aeration and to support the temperature sensors ( Figure 2b). A detailed description of the bioreactors was reported in [11,24]. To optimize the efficient operational method for composting palm tree residues, one bioreactor was operated continuously (continuous aeration-rotation, D1), and three were operated for 20 min of aeration-rotation at 1, 2, and 3-hour intervals (D2, D3, and D4), respectively.…”

“…A similar experimental procedure was reported in [11,24]. For each bioreactor, compressed air (flow rate of 0.005 m 3 min −1 at 10-bar) was supplied to the horizontal tube which the bioreactor rotates around it.…”

“…These residues can be composted and used in the soil as growth media to improve the soil structure by increasing the organic matter of soil, thus improving the poor soil fertility in the desert of Saudi Arabia [8][9][10]. Enclosed composting Sustainability 2020, 12, 201 2 of 11 systems (rotary bioreactors) have proven to be an efficient technique in farm-scale composting or small projects, and are the most suitable composting systems to be used successfully in the Arabian Peninsula [11]. This is because of the dry climate, high daily water evaporation rate, and water shortage [12].…”

“…Aerobic conditions were maintained naturally by opening side doors in the drums half-way after the rotations were completed [14][15][16][17][18]. Continuous aeration-rotation was used for composting tomato plant residues mixed with chicken manure in a pilot-scale bioreactor with the aim of reducing the active phase period [11] and analyzing energy performance [24].…”

“…A literature survey of previous studies revealed that (i) studies on mechanically operated, intermittent aeration-rotation are very limited [11], (ii) composting in a rotating bioreactor depends mainly on the composted material and the combined aeration-rotation frequency, (iii) the impact of the combined aeration-rotation frequencies on the bioreactor performance and the composting process is still unclear, and (iv) studies on composting palm tree residues in a closed system or even in an open system (e.g., static pile, windrows) are not available. On the other hand, successful and effective composting requires a sufficient amount of oxygen via aeration, and requires adjusting control parameters such as the temperature of composting, the mixture moisture content (MC), and the carbon to nitrogen (C/N) ratio [25].…”