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Evaluation of compost maturity by hot water extracted (HWP) carbon

The water soluble carbon has been proposed by several researchers as a parameter to evaluate compost evolutionbecause its concentration rapidly decreased with the process. The authors established the 0.5 % value as a maximumcontent of water soluble carbon above which compost could be considered mature.The aim of this work was evaluate the hot water soluble carbon extracted with Hot Water Percolation (HWP) as anindicator of compost maturity stages.The composting windrow was built from green wastes on 10. October and destroyed on 21 November.

The outsidetemperature was above 10oC, and from 15 November about 5oC.The sampling times were 0, 2, 8, 16, 21, 30, 37 and 42 days after establishing the compost wíndrow. The depth ofsampling was 40 cm.Dry matter content, ignition loss (organic-C) and carbon content and spectral properties of HWP extracts weredetermined. The hot water percolation (HWP) is a new easily applicable soil extraction method (Füleky and Czinkota,1993) which was adapted to compost analysis. During hot water percolation the desorbable, hydrolizable and easilysoluble elements and compounds are extracted by hot water (102-105oC) at 120-150 KPa (Takács-Füleky, 2003). 5times 100 cm3 extracts were collected and TOC was determined in the solution. The optical density of these solutionswas measured at 254, 465 and 665 nm.During composting process the amount of total organic carbon significantly decreased. At the same time the hot watersoluble HWP-C content decreased from 605 mgL1 measured on the 0 day of composting to 27.9 mg L-1 on the 42 day. Itis a strong positive correlation between the HWP-C content of the first 100 cm3 fraction and the sum of 5 times/100 cm3fractions (R2 =0.9830). Consequently is enough to measure the carbon content and spectral properties of the first HWPfraction. The measured HWP-C content is naturally less than the measured value at other authors (0.5-1.7 %) becausethe hot water percolation (HWP) is a fast, one-two minutes long process. It is a very strong linear correlation betweenthe absorbance at 254 nm and the HWP-C content of extracts (R2=0.9545).The tendency of SUVA values is very similar as the results of Said Pollicino et al., 2007. Their results show a suddenincrease of SUVA after the 28 day of composting which means the maturity of compost. The E4/E6 values show thesame tendency which was demonstrated by Sellami et al., 2008, when the E4/E6 significantly decreases at the maturitystage. Both the HWP-C content measured in 100 cm3 and 5 times 100 cm3 extracts at 254 nm and also at 465 and 665nm show a decreasing tendency during maturation process.As a conclusion the HWP-C content, the absorbance at 254 nm and the E4/E6 values of hot water percolation (HWP) extracts very well show and demonstrate the maturity stages of composting process, in spite of the fast extraction.

Copyright:	© European Compost Network ECN e.V.
Quelle:	Orbit 2012 (Juni 2012)
Seiten:	6
Preis:	€ 6,00
Autor:	Dr. György Füleky
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