World generation of Municipal Solid Waste (MSW) is of the order of 17 billion t/year, and due to population growth and changes in consumption habits, has been predicted to increase up to 27 billion t/year by 2050 [
Composting is often considered a clean and ecological technology, as it represents a transformation of organic waste into nutrient-rich fertilizers through two phases, the mineralization and humification phases [
To reduce these limitations, it is common to incorporate co-substrates as amendment and/or bulking agents, such as green waste, and agro-industrial waste such as Sugarcane Filter Cake (SFC) or sugarcane bagasse [
These clarification products typically have no value and are placed directly in crops, but in some cases can lead to environmental problems such as Greenhouse Gas (GHG) emission and nutrient leaching [
In Brazil, India, and China 1.9 million tons of sugarcane are produced, on average generating 85.5 million tons of SFC [
Although SFC has traditionally been used in composting with agro-industrial waste, it has been little considered in composting with BW. In this research, the effect of incorporating SFC as an amendment material was evaluated, on a pilot scale, on the improvement of both, the BW composting process and the quality of the final product. The following characteristics were analyzed, nutritional: total nitrogen (TN), total potassium (TK) and total phosphorus (TP); agronomic: cation exchange capacity (CEC), electrical conductivity (EC), stability, maturity; and microbiological: total and fecal coliforms.
The materials evaluated in the composting process were:
The composting piles were formed in duplicate, with 150 kg and conical geometry. To determine the incidence of the incorporation of the SFC in BW composting, a unifactorial experimental design was carried out by considering the mixing ratio BW:SFC to be the only factor defined considering that
Process monitoring was carried out by monitoring the behavior of the variables temperature, moisture, pH, TOC, and TN. Temperature was monitored daily by using a 70 cm dial thermometer and the mean value recorded for the perimeter points and the centroid of each treatment was recorded as well. Moisture was measured every three days by gravimetry, while pH was determined daily by diluting 10g of sample in 50 mL of distilled water, using a WTW Model 315i meter. The TOC and TN were determined twice a week.
The aeration of the piles was carried out by manual turning, with a twice-a-week frequency during the first four weeks of the process, during which time, there is a greater microbial activity. Once this active (mesophilic and thermophilic) phases of the process had been completed, according to the temperature profiles in the treatments, the frequency of the tumbling was reduced to once a week [
At the end of the composting process, a manual sieving (1.25 cm sieve) of the products of each treatment [
The stability of the products was quantified with the Dynamic Respirometric Index (RI) [
As a complementary quality indicator, the fertility index (FI) was determined. Saha et al. [
Where
Finally, the characteristics of the products obtained were analyzed and compared with the Colombian technical standards NTC 5167 [
Regarding the BW, it was found that the TOC is lower than that reported in other studies (TOC <35%) and the TN is higher (> 1%) [
Regarding SFC, it presented a C/N ratio of 30.37 ± 2.58 due to the high TOC content and is similar to the value reported by Meunchang et al. [
Mean values; *sample size (n): 5. + simple size (n):3. hb: Humid base, db: Dry base, BW: Biowaste, SFC: Sugarcane Filter cake, (BW:SFC)
The treatments with the incorporation of SFC reached the thermophilic phase in less time (between 1 and 2 days) compared to the control treatment (3 days), which shows the synergistic effect of incorporating SFC in BW composting. The statistical analysis confirmed the existence of significant differences between the treatments with SFC (p=0.022) compared to the control (only BW). The time to reach thermophilic temperatures coincides with the results of authors such as Ogunwande et al. [
The highest temperature (67°C) was reached in treatment B2; however, all the treatments achieved hygienic conditions since they sustained temperatures equal to or greater than 55°C for at least four consecutive days [
The aforementioned is associated with a shorter duration of the cooling phase in B2 and B3, which confirms that the incorporation of SFC decreases the process time with respect to the control treatment, which coincides with that reported by Meunchang et al. [
The initial pH values for all the treatments ranged between 5.13 and 5.54 units (
The pH values at the end of the process ranged between 7.53 and 9.5 units. The most alkaline value was found in B1, a condition that could hinder the release of nutrients in the soil and plants [
In relation to TOC and TN, Figure 3 shows the behavior during the composting process. In
After day 40, the biodegradation of TOC tended to stabilize, which is associated with a probable decrease in biological activity, due to the easily degradable substrate being broken down during the active phase of the process. Waqas et al. [
From day 43 to day 79, there was a marked increase in TN, during which time the cooling phase occurred. This increase is associated with the mineralization of organic matter and the effect of concentration [
In summary, the analysis of the effect of the different variables on the process shows that the incorporation of SFC had a favorable effect on the composting of BW, with the proportion B2 (BW: SFC - 80:20) being the most favorable, presenting improved characteristics such as pH, higher content of nutrients and TOC.
Regarding pH, the products presented alkaline values (pH> 7.5). According to Lasaridi et al. [
All the treatments presented a CEC greater than 20 meq/100 g, that indicates that they would stimulate biological activity by the exchange of bases with the soil. The EC values are low in comparison with the limit proposed in the regulations and indicate little presence of salts, which is important to reduce phytotoxicity problems in plants [
Regarding the content of TOC, TNK, TP and TK, treatment B2 shows the highest potential for agricultural use, since it presents better nutrient content and agronomic characteristics such as CEC and EC. Consideringthe biological quality, all the SFC treatments presented stable conditions since they had an oxygen consumption lower than 1.0 mgO. gSV-1 [
The final product obtained (compost) from each of the evaluated treatments is considered mature (not phytotoxic) and with high fertilization potential according to the GI obtained during the germination tests with
In contrast, the BW composting product (control) and the B1 treatment had a lower GI and FI, indicating that these products can inhibit plant growth. Regarding microbiological quality, the products of all the treatments are Class A because the density of TC and FC is less than 1000 NMP / g.
BW are a substrate with high potential for composting; however, they are often deficient in nutrients such as phosphorus TP, TN and TOC. This deficiency can be compensated through the incorporation of an amendment material such as SFC, increasing both the amount of TOC and the amount of nutrients (TN and TP) and at the same time improving parameters such as CEC.
The performance of BW composting improved in the three treatments in which SFC was incorporated, reaching temperatures higher than 55°C and reducing the duration of the process when compared to the control treatment.
The treatment that complied with all the guidelines established by NTC 5167 was B2 (80% BW: 20% SFC), achieving medium-high concentrations (w/w) of organic matter (> 20%), TN (2.32%), TP (1.42%), TK (> 2%) and alkaline pH values (7.75), promoting radicle growth and/or the number of germinated seeds. Which gives it potential as an organic fertilizer in acid soils.
From the point of view of the final quality, the product (compost) obtained from each of the treatments is considered a mature product (not phytotoxic), according to both the GI and FI obtained during the germination tests carried out with
The authors would like to thank Universidad del Valle for funding the C.I. 2985. Conflicts of interest: This article was prepared and reviewed with the participation of all authors. We declare that there is no conflict of interest that puts the validity of the results presented at risk.
Research paper