The purpose of this study was to examine whether any environmental benefits were obtained when the emptying of sludge from septic tanks were carried out with a dewatering technique using polymers compared to complete pump-out. The mean value of transport distance, fuel consumption, CO2 emissions and the weight of waste per septic tank emptying was calculated for each emptying method. For this, data on transport distance, fuel consumption, CO2 emissions per liter of fuel and number of emptied septic tanks were used. An energy audit over a sewage treatment plant was used to calculate the energy consumption for the treatment of the waste from the two emptying techniques. The environmental impact of the use of polymers and the returning of reject water to the septic tank was examined by studying the literature in the research field. The result showed that emptying with a dewatering technique compared to complete pump-out resulted in shorter transports, less fuel consumption, lower CO2 emissions, less waste and a lower energy consumption for waste treatment. The use of polymers in sludge dewatering should not have any adverse effects on aquatic organisms or health impacts if the dosage and the design of the treatment plant is correct. It is not established whether the return of reject water have any environmental effects. In conclusion this report shows that the emptying of septic tanks with a dewatering technique is better than complete pump-out from an environmental point of view.

The purpose of the study was to evaluate which method for emptying of septic tanks that contributed with the lowest particle content in outgoing water during the period of a year. The methods for emptying in the comparison was mobile dewatering using polymer, complete pump-out and mobile dewatering using mechanic separation. Within the study, wastewater was sampled from septic tanks third compartment, however, only from septic tanks that were dewatered using polymer. Samples were taken one time before emptying followed by five occasions after emptying. The results from those samples were compared to previously existing results from complete pump-out and mobile dewatering using mechanic separation. Due to differences in method for sampling, the comparison in the discussion was limited to; samples taken before emptying and two weeks after emptying from septic tanks that had been completely pumped-out and dewatered using mechanic separation. The samples taken before emptying showed the particle content after using the septic tanks for a year since the previous emptying. Based on those samples there were no significant difference between mobile dewatering using polymer and complete pump-out or between mobile dewatering using polymer and mobile dewatering using mechanic separation. Two weeks after emptying the lowest particle contents were found in septic tanks that had been completely pumped-out followed by the two dewatering methods.