Spring 1997

Aquatech Europe

Alkaline sewage sludge stabilisation Waste Water Directive 91/271/EEC will result in a significant increase in sludge production in Portugal. Although the Directive does not impose secondary treatment for areas under 2000 inhabitants, it is considered for environmental reasons, that secondary treatment should be available to the total Portuguese population.Rhenipal products, specifically developed to facilitate the treatment of sewage sludge for landfill disposal, is currently being successfully applied at a regional treatment works/landfill at Alcenena in central Portugal. Following successful development and application in Germany, the UK and Czech Republic, a Development Project was agreed in 1994 between Tejo Energia (the owners of Portugal's Pego coal-fired power station), Rhenus AG (Germany) and DIRK Group Holdings Ltd. (UK) to assess and develop sewage sludge treatment for the Portuguese market. An extensive programme of trials and evaluations was carried out throughout 1994-5 at five (5) principal treatment works including Alcanena. The trials proved the technical abilities of the Rhenipal process and convinced potential customers that Rhenipal is the only viable solution for the immediate sewage sludge problems and for some of the problems faced by the Portuguese waste water industry. As a consequence, the Instituto da Agua (a division of the Ministry of Environment) announced in July 1995 an international public Tender to resolve one of Portugal's most urgent environmental sewage treatment problems at Alcanena. The Tender asked for alkaline stabilisation using " for example, Rhenipal ". Nearly all of the companies tendering offered the Rhenipal solution. The order was awarded by end September to Soares da Costa ( Oporto ), one of Portugal's largest civil works contractors. Works were undertaken in Spring/Summer 1996 using Rhenipal as the solidification additive, a Belgian operator, LMB Milieubescherming GmbH as sub-contractor and DIRK Group Holdings Ltd as Technical Advisors. The project The Association of the Alcanena leather industry (AUSTRA) is currently spending 500.000 cts (c2,200,000 ) per year for the proper treatment of their effluent. Approximately 30.000 m3 of sewage sludge cake had previously been deposited into inadequate landfill areas. Approximately 80.000 m3 of sewage cake had been placed into a lined lagoon without stabilisation. The new mono landfill for Rhenipal/Terrafix stabilised sludge has an expected lifespan of 15 years. A new landfill facility has been built by Soares da Costa s.a.. This landfill has been specifically designed to receive Rhenipal/Terrafix stabilised sludges removed from the above areas and the ongoing sludge production of the Alcanena sewage treatment works. This treatment works is currently undergoing a major extension programme to reach a sludge processing capacity of 11,500 dry tonnes /year. Elisa Ferreira, the Portuguese Minister of Environment visited the Rhenipal / Terrafix site in Alcanena and hailed the Rhenipal / Terrafix stabilisation process as a final solution to the problems.The population of Alcanena suffered for too long. On the 8th October, the Portuguese Television reported about the Minister's visit in the 8 pm TV news. The Minister said: "The Alcanena problem will disappear for good by March next year because the system applied now transforms the sludge or toxic residue into a drier and more inert matter." The first stage The previously disposed sludges are excavated from the disposal area and stabilised with Rhenipal/Terrafix, an alkaline stabilisation additive which contains pulverized fuel ashes supplied by PEGO Power Station, Portugal. PEGO is owned by TEJO Energia s.a. a joint venture of major European Power generators: National Power plc (UK), ENDESA s.a. (Spain), EDP s.a. (Portugal) and EDF (France). Dirk Group Holdings Ltd act as the senior consultant to Soares da Costa for the project.The quality control is provided by using Dirk's on-site laboratory. The treated cake that has been approved is then deposited into the new landfill using a technique and special equipment specified by the Dirk Group.The above treatment is also applied to the sewage cake produced by the sewage treatment work on a daily basis (approx. 60 m3 of dewatered cake per day) until the newly designed chamber press is installed. Rhenipal Portugal Ltd., which is part of the DIRK GROUP, with an office in Setubal , Portugal, was to provide a reliable, long term provision of the Rhenipal / Terrafix products and services. Peter Wilkinson,Managing Director of Rhenipal Portugal Ltd. stated: "Together with TEJO Energia we have jointly invested in research that proved that the Rhenipal/Terrafix process meets the environmental control parameters specified by the Portuguese Authorities (DGA) for safe disposal of stabilised sewage sludge cake. Dirk Group's special alliance with TEJO warrants the long term secure supply of a quality controlled Rhenipal/Terrafix product." The second stage Dirk Group recommended for the long term stabilisation process at the new sewage sludge de-watering facilities at Alcanena, either their post- or pre-stabilisation methods. Both methods will achieve the same secure end results. Further tests will determine the selection of the most favourable option. Whereas the post stabilisation method mixes dewatered sludge cake with Rhenipal /Terrafix, the pre- stabilisation method injects the Terrafix additive prior to the cake being dewatered. This process provides a substantial reduction of the stabilisation costs. Above picture: Mr. G. Dirk (chairman of DIRK Group) discussing the Rhenipal/Terrafix process with the Portuguese Minister of Environment: Mrs.Elisa Ferreira