Successful symposium on sewage sludge disposal and phosphorus recovery

The forum attracted great interest and finally counted more than 170 participants / Photo: HUBER

On 22nd November, the UmweltCluster symposium on sewage sludge disposal and phosphorus recovery took place on the premises of HUBER SE in Berching. HUBER organised the event together with UmweltCluster Bayern e.V. – a Bavarian environmental collaboration initiative – and German Phosphorus-Platform DPP.

The disposal of the sewage sludge that is generated from wastewater treatment in Germany costs about 500 million Euro per year. Up to now, sewage sludge disposal has meant that the sludge is either utilised as fertilizer being spread onto agricultural land or used for landscaping, or incinerated in power or cement works and mono-incineration plants.

But there is an amendment of the German Sewage Sludge Ordinance (AbfKlärV) coming up with far-reaching changes relating to the utilisation of sewage sludge. The amendment, which will presumably come into force in 2017, stipulates a significant reduction of the agricultural use of sewage sludge and commits larger sewage treatment plants (for more than 50,000 PE) to recover the phosphorus. In addition to promoting the recovery of valuable material, this legal regulation is intended to protect also the groundwater against further contamination by pharmaceutical residues.

This attracted great interest among sewage plant operators, operators of incineration plants, associations for sewage sludge utilisation, politics, engineering offices and research institutes. We finally counted more than 170 participants from Bavaria, Baden-Württemberg, Hesse and Austria.

They were welcomed by Mr. Mayr of the UmweltCluster Bavaria, Mr. Georg Huber, CEO of HUBER SE, and Dr. Schnee of the German Phosphorus-Platform. At the beginning, Dr. Schnee as the moderator of the event read out a statement of the Bavarian State Ministry for environment, health and consumer protection on the future requirements on sewage sludge disposal in Bavaria.

Prof. Bischof and Prof. Mocker of the University of Applied Sciences Amberg-Weiden in Eastern Bavaria presented a comprehensive overview on the present state of the Sewage Sludge Ordinance amendment and the options of phosphorus recovery on sewage treatment plants and from sewage sludge ash in general.

Dr. Markus Rödiger, consulting engineer from Stuttgart, reported about the energetic situation of small and medium-sized sewage treatment plants including sewage sludge drying in solar dryers and belt dryers. He also provided useful information how to fill energy gaps in advanced treatment.

Dr. Heindl of HUBER SE explained some of the highly efficient HUBER machines and described a possible scenario for phosphorus recovery in Bavaria. He explained that enough capacity would be available in Southern Bavaria for the thermal utilisation of sewage sludge whereas four new utilisation plants would have to be erected in Northern Bavaria, among other mono-incineration pants, preferably on existing power plant sites. The actual recovery of phosphorus from the ash could be done in two centres, among other by a private fertilizer processing and trading company.

Harald Plank of S2E GmbH, a subsidiary of HUBER SE and WTE Wassertechnik GmbH in Essen, informed about mono-incineration plants for the thermal utilisation of sewage sludge which have especially been designed as modular systems for dewatered sludge volumes of approx. 10,000 to 50.000 t/year. These plants are offered as complete systems including sludge storage, drying, incineration and storage of ash in a building.

With great anticipation the audience had waited for what Thomas Knoll, Managing Director of the joint waste management authority Schwandorf, would tell about a very special project. He reported of a merger of several municipalities for thermal sewage sludge utilization which is unique so far and takes over the drying of the generated sewage sludges, among other those of the city of Regensburg. A new belt drying plant is planned to dry the sludge on the site of the waste-fired power plant in Schwandorf using exhaust heat. The dried sludge is planned to be co-incinerated in a nearby cement works.

A site report of phosphorus recovery from ash was presented by Bernhard Ortwein of CNP-Technology Water and Biosolids GmbH. Sewage treatment plants with biological phosphorus elmination frequently have problems with phosphate deposits in the pipelines downstream of the digester. The AirPrex system prevents such operational problems through phosphate removal from the sludge liquor and, as a side effect, produces fertilizer in the form of magnesium-ammonium phosphate.

Burghard Hagspiel of Stadtentwässerung Nürnberg (authority for waste water and surface water collection and treatment) reported about the latest state of the research project KRN-Mephrec on STP Nuremberg. The sludge there is dried and briquetted. Coke and lime are added then and this mix is melt-gassed in a cupola furnace. The products that are won from the tap are metal and phosphate slag. Phosphate slag is a well plant-available fertilizer.

Michael Knust of WTE-Betriebsgesellschaft GmbH explained the sewage sludge disposal concept to be implemented on STP Hecklingen in Saxony-Anhalt. As a first step, a belt dryer will be installed. From 2018 on, it is planned to further operate a mono-incineration plant for sewage sludge as a BOT model.

Dr. Turek of MSE Mobile Schlammentwässerungs GmbH (Mobile Sludge Dewatering PLC) presented a mobile plant for phosphorus recovery from sewage sludge which is installed in two 40ft sea transport containers. In a wet-chemical process, magnesium-ammonium phosphate is won from the sludge which can be used as fertilizer after drying and granulation.

There were vivid discussions, particularly about the methods of recovering phosphorus from sludge or ash, the comparison of mono-incineration and co-incineration in cement works after prior phosphorus depletion and about the costs of the available techniques and how to implement them in practice.

The successful event ended with a tour of the HUBER factory.