Markku Pelkonen

Optimization of landfill leachate management in the aftercare period

The management of sanitary landfills after closure is an important engineering, economic and sustainability issue and is referred to as the greatest unresolved landfill challenge. Most sanitary landfills are operated according to the dry tomb principle, resulting in aftercare periods of hundreds of years. To study landfill body behaviour, long-term leachate emissions were studied with anaerobic landfill simulators, and a forecast model was developed targeting the behaviour of NH4-N, COD and chlorides as a function of temperature and the L/S-ratio (liquid-to-solid). It was found that NH4-N is the decisive factor in leachate management, requiring the highest L/S-ratio (around 6) to meet the direct discharge limit values. Various scenarios were constructed to find optimal leachate management strategies both in large (waste height H = 25 m) and medium-sized landfills (H = 10 m) with corresponding temperature ranges. The results show that by minimizing the aftercare period length with leachate pre-treatment and recirculation, both sustainability and economic benefits can be achieved. The results provide new views on how to manage the long-term leachate aftercare problem. In the case of large landfills, further efforts are needed to reach stabilization within a reasonable time frame.

Effects of Temperature on the Long-Term Behaviour of Waste Degradation,Emissions and Post-Closure Management Based on Landfill Simulators

A demonstration pilot with seven anaerobic landfill simulators (LSRs) was used to study the impact of temperature in the range of 20 - 46 °C on long-term landfill emissions, characteristics and tendencies, because of an evident lack of knowledge in this area. The pilot ran more than 1400 days. Higher temperatures accelerated the waste degradation and gas generation, but also resulted in higher leachate COD and NH4-N concentrations, which will prolong the aftercare period in order to meet the effluent discharge limits. Gas generation showed the highest temperature sensitivity, 1.6- 2.8 % o C -1 , whereas COD, NH4-N and chloride emissions were on 0.8 - 1.5 % o C -1 level. The temperature coefficient of gas generation differs considerably from the scarce values given in landfill simulation studies, but is in accordance with hydrolysis solubilisation related behaviour and gives thus more detailed information of landfill behaviour at different temperatures. The simulator results were applied in European conditions in a typical big landfill containing mainly organic matter, giving the length of aftercare over 200 years to achieve effluent discharge limits. Within the same aftercare period (around 200 years), mesophilic conditions compromised high gas production and near lowest leachate concentrations. The in situ landfill leachate pre-treatment process and a specific leachate management system are essential in order to achieve cost-effective and shorter landfill aftercare. The results give new information for evaluation and modelling of landfill control strategies in long-term in various environmental conditions.

Cost-saving biological nitrogen removal from strong ammonia landfill leachate

The aim of the study was to develop an improved management mode in Ämmässuo landfill (Finland) for leachate ammonium-nitrogen removal, to minimize the leachate management costs and secure compliance with the uptrend requirements of regulations for on-site leachate management. With a single sequential batch simulation reactor, the minimum C/N ratio was detected as 1.7 (adjusted by external carbon addition), to achieve the acceptable removal efficiency of 99, 62 and 74% in NH 4-N, total nitrogen and chemical oxygen demand, respectively. Both total nitrogen removal and efficiency of carbon use were correlated with an increasing NO- 2 /NO- x ratio indicating higher performance with denitrification via nitrite. It was estimated that the leachate management cost could be reduced by 28 to 38%.

Online identification of activated sludge settling properties

Abstract Activated sludge settling properties can be characterised with two time-varying parameters. A simple method is presented for online identification of these parameters. The method is obtained as an exact solution of the filtration problem; it is obtained on the basis of the settling process description and the parameters variation process description. The method is suitable for practical application. It is a more exact solution of the identification problem than the alternative regression analysis method. An easily implementable system is proposed for automatic characterisation of the sludge settling properties.

Activated sludge concentration dynamics

Abstract The relationship between activated sludge concentration in the aeration and settling tank is determined on the basis of settling process characteristics. The relationship is used for description of the activated sludge concentration and stock dynamics in the aeration and settling tank. A limit value for maximization of activated sludge concentration is determined.