MechChem Africa February 2020

Wastewater from milk processing at Milchwerk Jäger GmbH used to be discharged to the public sewer system and treated at the local municipal sewage treatment plant, until the plant reached its capacity. HUBER was tasked with verifying the operation of a membrane bioreactor (MBR) system using the HUBER BioMem plant, and reviewing the nitrogen reduction rates in the whey treatment process on the premises. Water treatment in the dairy industry – development of customised solutions for direct and indirect discharge

M ilchwerk Jäger GmbH is the oldest private dairy company in Germany, operating a milk- processing factory at Haag in Upper Bavaria, southeast of Munich. With the company’smilk catchment area extending into Austria, the company produces mainly Italian-style cheeses and butter for export. The waste generated during production is mainly wastewater from traditional milk processing – which includes a high fat con- tent and vapour condensates – and perme- ates from the milk powder drying process. Previously, the wastewater was discharged to the public sewer system and treated with the town’s wastewater at the local municipal sewage treatment plant until, owing to the company’s continuously growing production, it could no longer meet the effluent limits set by authorities. The available alternatives were either to expand the municipal sewage treatment plant, with a high financial contribution from Milchwerk Jäger GmbH, or to build a com- pletelynewplantforfullorpartialwastewater treatment. The planning office commissioned to examine possible variants, and do some preliminary planning, carried out pilot tests where it was established that, owing to lim-

ited space and special characteristics of the vapour condensates andwheypermeates, the best option would be to insert a membrane bioreactor systeminto theexisting infrastruc- ture/treatment plant. Preliminary pilot testing with the MBR system The wastewater, reduction properties and general suitability of the MBR system for the wastewater were tested on a HUBER Membrane Filtration BioMem ® pilot plant. The key component of the plant is the membrane bioreactor, a combined tank in which the processes of biological contami- nant removal and membrane filtration with ultrafiltration modules take place quasi- simultaneously. To allow for fully automatic plant operation, blowers, pumps and controls are provided as associated equipment for the tank chamber. Different variants of deni- trification can be tested with intelligent op- eration modes of plant feeding. All operating parameters are logged by the control system, and chemical parameters are analysed in the company’s laboratory. The test plant was installed at the end of 2015 and, after a short adaptation phase, operated until April 2016. Intermediate data

and the resulting adjustments during the ad- aptation phasewere regularly discussedwith the plant operators and planners. The wastewater was first put into a small buffer tank so that, later, the actual wastewa- ter composition could be better simulated. Furthermore, all plant components were insulated and heated to prevent freezing in winter. Automatic sampling devices were installed to obtain representative composite samples fromthe buffer tank and effluent. As a result of the low chemical oxygen demand (COD) values related to thenitrogen, residual wheywasmixedintotheinfluenttoenablethe complete degradationof nitrogen in the deni- trification phase. Furthermore, a sodium hy- droxide solutionwas added regularly to keep the pH values neutral – a basic requirement forthebiologicaldegradationofcontaminants and a stable sludge structure in an MBR. COD degradation TheCOD inlet concentrations varied from20 to 200mg/l andwere generally low to ensure both the basicmetabolic rate of themicro-or- ganisms anddenitrification. Available residual whey with a COD of approximately 30 000 to 40 000 mg/l, or whey semi-concentrate of approximately 60 000 to 80 000 mg/l re- spectively, was added as an external carbon source. The COD concentration in the efflu- ent from the plant was, with few exceptions, constantly below 10 mg/l. This value was significantly below the limit concentrations for direct discharge or infiltration. Phosphate reduction The concentrations of total phosphate were between 5 and 20mg/l in the inlet. The outlet concentrations were higher than the inlet concentrations, possiblydue to thephosphate entering the plant with the whey. At theendof the test phase, the total phos- phate in the outlet was permanently below 1 mg/l. The team concluded, however, that a permanent installation should include simul- taneousprecipitation toensure theapplicable effluent requirements could be reliably met. Conversion and reduction of nitrogen Following a short operation phase, the am- monium nitrogen was converted into nitrate nitrogen through a process of nitrification.

HUBER Membrane Filtration BioMem ® demo unit for the determination of design parameters (photo not taken at Milchwerk Jäger GmbH).

20 ¦ MechChem Africa • February 2020