The invention is concerned with a batch method for obtaining crystallized lactose and arrangement configured for executing the method. The method comprises obtaining initially from a lactose crystallization process mother liquor and wash water generated in that process. The obtained mother liquor and wash water are collected and not discarded. Thereafter the collected mother liquor and wash water are subjected to purification and concentration in a batch process contrary to the known continuous processes performed independently of the lactose crystallization process. Aqueous solutions comprising lactose obtained as a result of the independent purification and concentration process accordingly comprise reduced amounts of the impurities usually comprised in the by products of the lactose crystallization process. The aqueous solution comprising lactose can then be collected and re used as a lactose source in a lactose crystallization process either on the same process equipment which supplied the original batch or on separate equipment. The method of the invention minimizes loss of lactose in one or more waste streams.
