The treatment performance and nitrogen mass balance of a pilot-scale landfill leachate treatment system was evaluated. The system was comprised of a series of three ponds and a rock filter and was fed a continuous flow (200 L d(-1)) during 111 weeks. Three different operational conditions were investigated: conventional operation (stage I), aeration (stage II) and aeration/recirculation (stage III). The system was able to treat landfill leachate with soluble chemical oxygen demand and ammonia removal between 35-82% and 75-99%, respectively, and the highest removal occurred during the recirculation stage. The nitrogen balance was calculated using total nitrogen applied load and the main transformation processes within the ponds. The main form of nitrogen transformation/removal was by dead/inert algae settle (64-79%), followed by volatilization (12-27%) and algae assimilation (1-6%). Nitrification/denitrification occurred in only stage II. Analyses of the phytoplankton community showed that the Chlamydomonas genera were dominant in the photosynthetic ponds.

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-The following sludge reduction alternatives were tested in wastewater biological reactors: oxic-settling-anaerobic (OSA-process); ultrasonic disintegration (UD); chlorination (CH); 3,3',4',5-tetrachlorosalicylanilide (TCS); and folic acid (FA). Compared to the control system, UD reduced 55% of the sludge production, and greater substrate and nutrient removal efficiency was achieved. CH worsened the sludge settleability and increased the SVI values; the system achieved 25% of sludge reduction. OSA showed 50% and 60% of sludge reduction after 16 and 10 hours under anaerobic conditions, respectively. The observed sludge yield during TCS addition was decreased by 40%, and the sludge settleability worsened. FA presented the highest sludge reduction (75%), and the system improved the nutrient removal efficiency by 30% compared to the control system and maintained the sludge properties. Acute toxicity conducted with Daphnia magna classified the effluent from the sludge reduction systems as non-toxic for discharge into water sources.

O objetivo deste estudo foi avaliar o desempenho de um sistema de tratamento de lixiviado de aterro sanitário, em escala piloto, formado por três lagoas em série (L1, L2 e L3) seguidas por um filtro de pedras (FP). Foram estudadas três condições operacionais, verificando-se o efeito da recirculação do efluente da L3 para a L1: 0, 50 e 100% da vazão. O sistema absorveu bem as flutuações de cargas, apresentando remoções superiores a 80% para DBO F, 70% para DQO T e 98% para nitrogênio amoniacal. Na lagoa L2 houve nitrificação parcial, com acúmulo de nitritos. Ocorreu presença marcante do gênero Chlamydomonas nas lagoas L2 e L3 fotossintéticas. Observou-se diminuição da toxicidade do lixiviado, com reduções superiores a 95% na saída do sistema. A melhor eficiência de remoção para as três condições operacionais estudadas foi obtida com 100% de recirculação.