Sains Malaysiana 44(4)(2015): 517–527

Life Cycle Inventory of Institutional Medium-scaled Co-composting of Food Waste and Yard Waste in Tropical Country

(Inventori Kitaran Hidup di Institusi pada Skala Sederhana Pengkomposan bersama Sisa Makanan dan Sisa Lapangan di Negara Tropika)

CHEE GUAN NG* & SUMIANI YUSOFF

Department of Civil Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

Received: 19 September 2013/Accepted: 19 October 2014

ABSTRACT

The main objective of the present study was to provide a comprehensive LCI of medium scale composting of food waste and yard waste at institutional level, based on substance flow analysis (SFA). A secondary objective was to present the composition and assess the quality of the final compost product from composting of typical Asian organic waste (food waste and yard waste). The experiments were designed to represent a batch situation in an institutional medium size composting scenario with input material of food waste mixed with grass clippings and dried leaves. Two composting runs were carried out with the intention to showcase the heterogeneity of organic waste and study the effect of windrow size on the performance of the process. The input and output material were sampled and characterized in order to quantify the substance balance of the process. SFA was performed by means of the mass balance model STAN 2.5 to compute unknown parameters (gaseous emissions). SFAs have been performed for C, N, K, P, Cd, Cr, Cu, Ni and Pb. The composting windrows were fed with 212.4 and 393 kg, respectively. VS content reduction is greater in composting pile with larger size (Run 2). The loss of C during composting was recorded in the range of 0.146-0.166 kg/kg ww. The C losses via leachate were insignificant (0.02% of the total input C). The total N loss during the process was 0.005-0.012 kg/kg ww. The leachate generation was measured as 0.012-0.013 kg/kg ww. The flows of selected heavy metals were assessed. Heavy metals were of minor significance due to low concentrations in the inputs (food waste and yard waste). Heavy metals were found to be released to the atmosphere. However, majority of heavy metals remain in the finished compost. The C/N reduction during the process was in the range of 10-23%. In general, the compost composition was considered to be within the ranges previously reported in literature and thus ready for application in gardening. The LCI presented in the present study can be used as a starting point for making environmental assessments of medium-scale co-composting of food waste and yard waste in tropical environment. No major environmental problems were identified from the process, except for the emissions of GHGs.

Keywords: Composting; direct emissions; food waste; life cycle inventory; substance flow analysis; yard waste

ABSTRAK

Objektif utama kajian ini adalah untuk memberi LCI yang komprehensif pada skala sederhana pengkomposan sisa makanan dan sisa lapangan pada peringkat institusi, berdasarkan pada analisis aliran bahan (SFA). Objektif kedua adalah untuk membentangkan komposisi dan menilai kualiti produk akhir daripada pengkomposan sisa organik tipikal Asia (sisa makanan dan sisa lapangan). Eksperimen direka untuk mewakili situasi kumpulan di institusi dengan senario pengkomposan saiz sederhana dengan input bahan sisa makanan yang bercampur dengan keratan rumput dan daun kering. Dua pusingan pengkomposan telah dijalankan dengan tujuan untuk menunjukkan keheterogenan sisa organik dan mengkaji kesan saiz timbunan ke atas prestasi proses. Bahan input dan output yang telah disampel dan dicirikan untuk menentukan baki bahan proses. SFA telah dijalankan melalui imbangan jisim model STAN 2.5 untuk mengira parameter yang tidak diketahui (pelepasan gas). SFAs telah dijalankan bagi C, N, K, P, Cd, Cr, Cu, Ni dan Pb. Timbunan pengkomposan masing-masing diberikan 212.4 dan 393 kg. Pengurangan kandungan VS adalah lebih besar dalam timbunan pengkomposan dengan saiz yang lebih besar (Pusingan 2). Kehilangan C semasa pengkomposan direkod dalam julat antara 0.146 dan 0.166 kg/kg ww. Kehilangan C melalui larut lesap adalah tidak ketara (0.02% daripada jumlah input C). Jumlah kehilangan N semasa proses adalah 0.005-0.012 kg/kg ww. Penghasilan larut lesap adalah sebanyak 0.012-0.013 kg/kg ww. Aliran logam berat terpilih turut dinilai. Logam berat tidak ketara disebabkan kepekatan yang rendah dalam input (sisa makanan dan sisa lapangan). Logam berat dilepaskan ke atmosfera. Walau bagaimanapun, kebanyakan logam berat kekal dalam hasil pengkomposan. Pengurangan C/N semasa proses adalah dalam lingkungan 10-23%. Secara umum, komposisi pengkomposan dianggap berada dalam julat seperti yang dilaporkan dalam kajian sebelum ini dan sekali gus bersedia untuk digunakan dalam berkebun. LCI yang dikemukakan dalam kajian ini boleh digunakan sebagai titik permulaan untuk menjadikan penilaian alam sekitar pada skala sederhana pengkomposan bersama sisa makanan dan sisa lapangan dalam persekitaran tropika. Tiada masalah alam sekitar yang utama dikenal pasti daripada proses tersebut, kecuali pelepasan GHG.

Kata kunci: Analisis aliran bahan; inventori kitaran hidup; pelepasan langsung; pengkomposan; sisa lapangan; sisa makanan

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*Corresponding author; email: guancher@hotmail.com