title: Treatment of chitin production wastewater with a combined process of chitosan coagulation and anaerobic-anoxic-oxic biofilm reactors
Creators: name: Tran, Nguyen Van Nhi
Publisher: name: Griffith University
Year: 2021
Subjects: subject: environmentally friendly
subject: chitin manufacturing
subject: Vietnam
subject: bio-coagulant chitosan
subject: anaerobic-anoxic-oxic biofilm reactor system

description: Along with the rapid development of the seafood processing industry in Vietnam, thousands of tons of seafood scraps are generated annually. One of the major seafood processing wastes is shrimp waste, estimated at over 100,000 tons per year. This huge amount of shrimp waste contains over 4,000 tons of pure chitin, a natural long-chain polymer of N-acetylglucosamine which can be deacetylated to form chitosan. Chitin is widely and increasingly used in animal feed production. The current domestic chitin production process in Vietnam is based mainly on the inorganic chemical method, including demineralisation with HCl, deacetylation and deproteination with NaOH, and colour elimination with NaOCl or other active oxidising compounds. This production process then generates acid and alkaline wastes, containing high levels of nutrients such as protein, astaxanthin, lipid, and high salt concentrations, causing environmental pollution or costly wastewater treatment. Therefore, an environmentally friendly chitin manufacturing is urgently required in Vietnam. The thesis focused on two main contents: the use of bio-coagulant chitosan, and an anaerobic-anoxic-oxic biofilm reactor system. Firstly, chitosan application as a bio-coagulant minimised the amount of suspended solid wastes in chitin wastewater. This solution was more advantageous than coagulation by conventional chemicals because it was safe and environmentally friendly and economically profitable if sludge was utilised as animal feed and/or fertiliser. Secondly, wastewater was treated by anaerobic-anoxic-oxic biofilm reactor system using stick-bed biofix and swim-bed biofringe carriers to meet the technical regulation of wastewater discharge QCVN 11-MT:2015/BTNMT. The characteristics of chitin wastewater in the individual or mixed waste streams were first investigated. This assessment can help chitin producers recover valuable residuals in waste streams and simultaneously reduce the organic load in the wastewater treatment system. A pre-treatment process consisting of sedimentation followed by coagulation by by-product chitosan was conducted to evaluate chitin wastewater treatment and the crude protein recovery potential. The effluent after the coagulation-flocculation process was further run through biofilm reactors. This system needed microorganisms fully adapted to salinity and existing nutrient contents in chitin wastewater. The complete operating system on the laboratory scale could contribute as the foundation to the application in larger industrial scales. Experimental results showed that as chitin production processes reused the extracted chemicals and waste streams, the level of wastewater pollution increased. More of the soluble proteins were removed in the biochemical process than in the chemical methods. The waste streams' contents fluctuated remarkably depending on the nature of the input materials and the production process. For these reasons, the treatment of chitin wastewater confronted many difficulties. In addition, some technical-analytical results are listed as follows (a) Preliminary sedimentation removed over 80% of turbidity at pH 4, 30 mins of settling time, tCOD reduced by 39%, and TSS reduced by 93% (b) Optimal coagulation with by-product chitosan was achieved with the ratio between crude protein and calcium at around 5, chitosan concentration = 77.5 mgL-1, pH = 8.3, the reduction rates for the different parameters were as follow: tCOD (23%), sCOD (32%), TKN and NH4+-N (25%), TP (90%), TSS (84%), Ca2+ (29%), and crude protein (25%). (c) Chitosan was the most effective coagulant at lower ratios than other chemical coagulants in removing inorganic and organic chitin wastewater substances. (d) Crude protein content recovery was up to 55 mgg-1, and recovery of mineral content was around 10%. (e) The acclimation process running through three phases with gradually increasing input loadings from 1.5 kgCOD m-3d-1 to 2.5 kgCOD m-3d-1, removed over 90% of COD, 75-85% of TN and around 50% of TP. (f) The main treatment process of biofilm reactors going through five phases with the input loading increased from 3.0 kgCOD m-3d-1 to 6.0 kgCOD m-3d-1, flow rates from 12.96 Ld-1 to 16.4 Ld-1, and salinity from 6 ppt to 18 ppt. At phase 4 (loading of 5.7 kgCOD m-3d-1 and salinity of 14 ppt), the treatment efficiency reached over 90% for COD, about 60% for TN and TP, and 65% for calcium. Most of the processing efficiencies were high, making the treated wastewater meet the Vietnamese standard QCVN 11-MT:2015/BTNMT.