Resource Utilization Of Pickled Mustard Tuber Processing Water

A large amount of water is consumed and discharged in the food industry.The processing water has a high level of chemical oxygen demand(COD)due to the abundant organic matters,which causes serious resource waste and environmental pollution.For example,in the pickling industry,the processing water of pickled mustard tuber(Brassica juncea var.tumida Tsen et Lee)with high salinity contains lots of nutrients from mustard,leading to the extremely high COD value,which makes the treatment very difficult.At present,complex biological treatments and expensive membrane technologies have been used to treat this kind of processing water to reach the standard of discharge,however still cause environmental pressure and economic loss.Therefore,the purpose of this research is to design a relatively simple process for the recycle of low-salinity rinse water,and to prepare coarse salt by evaporation from high-salinity pickled water for reducing wastewater discharge and conserving resources.(1)Analysis of water quality of mustard rinse water and pickled water Two kinds of main processing waters during pickled mustard tuber production,high-salinity pickled water and low-salinity rinse water,were collected and analyzed for their water quality.The pickled water,with its salinity as high as 16.80-19.20%,had much suspended matter and special flavor with high value of chroma and turbidity;while the rinse water with its salinity between 3.20%and 4.80%,was relatively clear with light flavor,and the chroma and turbidity value were low.COD value of the pickled water and rinse water are as high as 21842.27-40032.13 mg/L and 4110.41-9264.64 mg/L,respectively.Amino acids were found to be the main factor contributing to COD value.According to these results,rinse water was reused by electrodialysis(ED),and pickled water was reused for its salt.(2)Design of ED desalination process for reuse of rinse water With its low salinity and large amount,rinse water was considered to be desalted and recycled after ED desalination.After the ED pilot-scale experiment,the test was amplified to pre-industrial scale with the treatment capacity at 200 L/h(6kg/h).Relative parameters,including operating pressure difference and operating current,were studied for their effects on the recovery rate of light brine and desalting energy.The results showed that the recovery rate of light brine and energy consumption were respectively affected by the operating pressure difference and operating current.Finally,based on the economic accounting,0.010 MPa and 25 A were the optimal desalting conditions,and under such condition,the cost was around 20 yuan per ton respectively.The recovery rate of the diluted water with salinity of I%reached 70%.In addition,it was indicated that a large number of amino acids,migrated from the side of concentrated water to the side of diluted water for operating pressure during the desalination process,resulting in an unintended increase of COD value.However these amino acids were derived from the mustard,thus the diluted water could be reused after sterilization.(3)Pickled water reuse for pickles making and coarse salt recovery High-salted pickled water is rich in nutrients.Two attempts,high-salinity water recovery for pickles making and evaporation for coarse salt recovery,were made for recycling.The results of the pickles test showed that the pickles obtained by diluting pickled water were more efficient in carbon source utilization by showing more organic acids,amino nitrogen and volatile constituents and less nitrite compared with the control group,which was under 5%salt water fermentation.The sensory evaluation indicated that the quality of pickles fermented in diluted pickled water was better than that of the control group.Results also showed that the pickled water could shorten the fermentation cycle so that it might be an ideal vegetable pickling material for practical application.On the other hand,the crude salt produced by evaporation with rich sugar content at 17.02 mg/g and amino acid content at 98.33 mg/g,could be used as animal salt licks,compound feed or food seasoning materials.