Nitrification of high-strength ammonium landfill leachate for improvement of river water quality in Malaysia
The mature landfill leachate is characterized by high-strength ammonium, which leads todifficulties in reducing the ammonium concentration in the wastewater discharge to the permissiblelimit (10 mg/L) using the existing biological treatment of sequencing batch reactors(SBRs). The challenge of the ni...
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| Format: | thesis |
| Language: | eng |
| Published: |
2019
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| Online Access: | https://ir.upsi.edu.my/detailsg.php?det=5629 |
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| Summary: | The mature landfill leachate is characterized by high-strength ammonium, which leads todifficulties in reducing the ammonium concentration in the wastewater discharge to the permissiblelimit (10 mg/L) using the existing biological treatment of sequencing batch reactors(SBRs). The challenge of the nitrogen removal via nitrification of high strengthammonium landfill leachate is substrate inhibition, particularly in the form of freeammonia (FA) and free nitrous acid (FNA) in ammonia-oxidizing bacteria (AOB) andnitrite-oxidizing bacteria (NOB). The problem is more severe, as 43% of the landfills are notwell designed and not properly equipped with leachate control mechanism facilities. In particular, this type of landfill exposed the river water to the risk ofammonium contamination from the landfill leachate. Therefore, there is an urgent need to improvethe existing leachate management at landfills.Prior to the nitrification study, leachate characteristics and the presence of inorganicnitrogen in the rivers receiving landfill leachate from three different types of landfills inSelangor state, Malaysia were assessed throughout a year to determine the impact oflandfill leachate on river water chemistry. In response to the results of the water qualitystudy, a nitrification-activated sludge system has been developed for high-strengthammonium synthetic wastewater, which serves as a reference before treatment with theactual landfill leachate. The system was operated under controlled conditions that favornitrification and was started in the fed-batch mode of operation to prevent inhibitoryeffects of FA and FNA on nitrifiers. As the heterotrophs could also inhibit the nitrification performance, the organic carbon removal was monitored during the nitrification of mature landfill leachate. A molecular technique, fluorescence insitu hybridization (FISH), was used to identify both the microbial populations as well as thelocalization of the nitrifiers in the sludge floe complex community.The background, scope and objectives of the study are described in the introduction, Chapter 1.In Chapter 2, leachates from three different types of landfills, namely active uncontrolled, active controlled and closed controlled, were characterized, and their relationships with river water chemistry were examined each month for a year. Theinfluence of leachate on river water chemistry from each type of landfill depended onmany factors, including the presence of a leachate control mechanism, leachatecharacteristics, precipitation, surface run-off and the applied treatment. The impact ofleachate from an active uncontrolled landfill was the highest, as the organic content, NNH/ Cd and Mn levels appeared high in the river. At the same time, influences ofleachate were also observed from both types of controlled landfills in the form ofinorganic nitrogen (N-NH/, N-NO-3 and N-NO?) and heavy metals (Fe, Cr, Ni and Mn).Improper treatment practice led to high levels of some contaminants in the stream nearthe closed controlled landfill.In Chapter 3, the feasibility of a nitrifying activated sludge system to completelynitrify synthetic mature landfill leachate with N-NH/ concentration of 1452 mg/L wastested. The process started with a nit rogen loading rate (NLR) of 0.4 kgN-NH/ !m3/day in afed-batch mode to avoid any accumulation of the FA and FNA in the system, and the NLR wassubsequently gradually increased. Complete nitrification was achieved with a very high ammonium removal percentage (-100%). The maximum specific and volumetricnitrification rates obtained were 0.49 gN-NH/lg VSS/day and 3.0 kgN NH//m3/day, respectively, which were higher than those reported previously for ammonium-rich removal using an activated sludge system. The nitrifying sludge exhibited goodsettling characteristics of up to 36 mL/g VSS and a long solid retention time (SRT) ofmore than 53 days, which contributed to the success of the nitrification process. Thecoexistence and synthropic association of the AOB and NOB were observed using the FISH technique,which supported the results on complete nitrification obtained in the system. These findingswould be of prominent importance for further treatment of actual landfill leachate.In Chapter 4, nitrification of mature sanitary landfill leachate with high-strength NNH/ (1080-2350 mg/L) was performed in a 10 L continuous nitrification-activatedsludge reactor. During the entire period of study, dissolved oxygen and pH weremaintained at a minimum of 2.0 mg/L and 7.4-7.6, respectively. The nitrification system wasacclimatized with synthetic leachate for about 13 days before being fed with actual matureleachate. Successful nitrification was achieved with an approximately complete ammoniumremoval (99%) and a 96% conversion of N-NH/ to N-NO-3 . At the sametime, BOD removal of 85 to 95% and COD removal of 38-57% were accomplished. Themaximum volumetric and specific nitrification rates obtained were 2.56 kgN NH/lm3/day and 0.23 g N-NH/lg VSS/day, respectively, at a HRT of 12.7 hand SRT of50 days. Incomplete nitrification of 3.14 kg N-NH/ /m3/day with up to 460 mg/L of N NO2-built up in the system was encountered when operating at higher (NLRs). The inhibitoryeffect of FNA on nitrifiers rather than interspecies competition betweenheterotrophs and nitrifiers was believed to trigger the accumulation of N-NO- 2 .Results from FISH experiments, which revealed the disintegration of some AOB cell aggregatesinto single cells, further supported the inhibitory effect mentioned above. During thecomplete nitrification, the AOB and NOB were found in almost similar percentages, whilethe number of the AOB and NOB decreased and the heterotrophs dominated for the duration of theincomplete nitrification. |
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