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Agricultural potential of anaerobically digested industrial orange waste with and without aerobic post-treatment

Research output: Contribution to journalArticleScientificpeer-review


Original languageEnglish
Pages (from-to)85-94
Number of pages10
JournalEnvironmental Technology
Issue number1
Publication statusPublished - 1 Jan 2012
Publication typeA1 Journal article-refereed


The potential of anaerobically digested orange waste with (AAD) and without (AD) aerobic post-treatment for use in agriculture was evaluated through chemical analyses, short-term phytotoxicity and long-term plant assays. Chemical analyses showed that AD contained ammonia and organic acids, and aerobic post-treatment did not significantly remove these phytotoxins. The N:P 2O 5:K 2O ratio in AD was 1:0.26:0.96 and aerobic post-treatment did not change the composition in AAD except for K 2O (1:0.26:1.24). Heavy metal contents in AD and AAD were more or less the same and were below the upper limit recommended for non-sewage sludge application on agricultural soils. Short-term phytotoxicity tests showed that seed germination and root elongation of Chinese cabbage and ryegrass were severely inhibited at digestate concentrations of 60-100%. Germination index values were well below the score of 50% required to indicate the phytotoxic-free nature of compost. Long-term plant assays showed that AD and AAD, when supplemented with a base fertilizer, resulted in higher plant growth, and fresh weight and dry matter production than AD without base fertilizer. The results thus indicate that aerobic post-treatment did not have any significant beneficial effect on reducing phytotoxicity, and AD could be used as such on agricultural soils, especially with high P.


  • aerobic post-treatment, anaerobic digestate, orange waste, phytotoxicity, plant assays