Toxicity evaluation of collagen hydrolysates from chrome shavings and their potential use in the preparation of amino acid fertilizer for crop growth

Resource utilization of chrome shavings(CS)has attracted a lot of attention from scientists and technologists in leather industry.Especially,the collagen hydrolysates extracted from CS are expected to find potential application values in agricultural field.However,there is no biotoxicity analysis of collagen hydrolysates from CS.Herein,the collagen hydrolysates with different molecular weights were produced from CS by three hydrolysis dechroming methods including alkaline hydrolysis,enzymatic hydrolysis and alkaline-enzymatic synergistic hydrolysis,and the optimal hydrolysis process of CS was designed and conducted.To evaluate their toxicity,the three collagen hydrolysates were formulated into a nutrient solution for zebrafish development.The obtained results indicated that the hydrolysates with low concentrations(less than 0.6 mg/mL)were safe and could promote the development for zebrafish embryos.Furthermore,the three collagen hydrolysates were utilized as organic nitrogen sources and formulated into amino acid water-soluble fertilizers(AAWSF)including alkaline type fertilizer(OH),enzymatic type fertilizer(M)and alkaline-enzymatic type fertilizer(OH-M)for the early soilless seeding cultivation of wheat,soybean and rapeseed.It is worth mentioning that the chromium contents in the prepared AAWSF were less than 10 mg/kg,which is far less than the limit value in the standard(China,50 mg/kg).The growth and development of seedlings(germination rate,plant height,fresh weight of leaves,soluble sugar content and chlorophyll content)were investigated.The corresponding results showed that the growth of seedlings watered with AAWSF was better compared with the other treatments,and the OH-M fertilizer had the best promoting effect on the seedlings growth and development,followed by the M and OH fertilizers.The safe toxicity assessment of the collagen hydrolysates will expand their application scope,and the use of collagen hydrolysates extracted from CS for seedlings growth also provides an effective and reason-able way to deal with the chromium-containing leather solid waste,which is an effective way to realize its resource utilization.

A combined kinetic study on the pyrolysis of chrome shavings by thermogravimetry

Chrome shavings(CS),a kind of solid wastes discharged from tanneries,always pose serious environmental problems due to the presence of chromium.In this work,kinetic study of the pyrolysis of CS was investigated using a thermogravimetric analyzer in nitrogen atmosphere.The results obtained from the thermogravimetric analysis indicated that there are three stages in the temperature range 25 to 600℃.The second stage is the main weight loss stage and it could be mainly attributed to the pyrolysis of collagenous materials.Iso-conversional and generalized master-plots method were first employed to estimate the activation energy value and possible reaction mechanism of CS pyrolysis.The results showed that the pyrolysis process could not be described accurately by single-step reaction due to the heterogeneous nature of CS.Afterwards,the thermogravimetric kinetic of CS pyrolysis was studied using combined kinetic analysis.It was found that three-parallel-reaction model allowed better fitting relevance for CS pyrolysis.This information was important for simulating and predicting the pyrolysis behaviors of CS.