Evaluation of GLDA-acid on sludge treatment effect and seed germination analysis

Mixtures of N, N-bis(carboxymethyl)-L-glutamic acid tetrasodium salt (GLDA) with citric acid (CA), glutamic acid (GLU), and aspartic acid (ASP) at the optimal proportion of 1:1, 1:2, and 2:1, respectively. They were employed for heavy metal removal from the sludge. The removal rate of common heavy metals (Cu, Pb, Zn, Ni, Cr, and Cd) and the retention degree of nutrients (total nitrogen, total phosphorus, available-N, Olsen-P, and organic matter) in the treated sludge were analyzed. Fuzzy comprehensive evaluation of the sludge was performed using MATLAB to determine the agricultural grade of the sludge. The sludge after GLDA-acid treatment was mixed with soil at different proportions, and Chinese cabbage, cucumber, and wheat were cultured. SPSS was used for survival analysis to analyze the feasibility of the sludge agriculture. The results showed that the optimal ratio of GLDA-CA and GLDA-GLU was 1:2 and that of GLDA-ASP was 1:1. After GLDA-acid treatment, the sludge was classified as Grade A agricultural sludge based on MATLAB fuzzy comprehensive evaluation and analysis. When the amount of sludge added was 20%, the growth of Chinese cabbage, cucumber, and wheat was promoted. Survival analysis further proved that the amount of sludge only affected the median germination time. Without considering the economic benefits, GLDA-acid can be preferred for sludge treatment, which can not only effectively remove heavy metals in sludge, but also have a small impact on agricultural use.