Graduation Year

2020

Document Type

Thesis

Degree

M.S.E.V.

Degree Name

MS in Environmental Engr. (M.S.E.V.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Sarina J. Ergas, Ph.D.

Committee Member

Mauricio E. Arias, Ph.D.

Committee Member

Qiong Zhang. Ph.D.

Keywords

Ammonia Nitrogen (NH4+-N), Chemical Oxygen Demand(COD), Ultra-Violet(UV) 456, Adsorption Media, Recirculating Biofilm Sequencing Batch Reactors (RB-SBRs)

Abstract

Leachate percolating through landfills must be collected and properly treated. However, high concentrations of ammonia (NH4+), refractory organic matter [measured as chemical oxygen demand (COD)], water color and heavy metals in leachate interfere biological processes in conventional wastewater treatment plants. Constructed wetlands (CWs) have been used in the past to treat leachate, but their design and performance has not been properly optimized. In particular, low cost adsorbent materials, such as zeolite and biochar, have the potential to adsorb ammonia and organic compounds, respectively. This increases their retention in the wetland and reduces their toxicity to microorganisms and plants in the ecosystem. In this study, three laboratory-scale recirculating biofilm sequencing batch reactors (RB-SBRs) were set up with the following media materials: 1) lightweight expanded clay aggregate (LECA), 2) LECA + clinoptilolite, a natural zeolite mineral (CZ), 3) LECA + zeolite + biochar (CZB). Reactors were operated in a four-stage sequence to simulate hybrid sub-surface flow wetlands: 1) fill, 2) anoxic react, 3) aerobic react, and 4) decant. The initial hydraulic retention time (HRT) was 14 days and was reduced to 8.75 days after 17 cycles. NH4+, COD, nitrite (NO2-), nitrate (NO3-) and UV456 absorbance were measured to compare the removal performance between RB-SBRs with and without absorbent addition. Substantially higher COD removal was observed in the biochar amended reactor. COD removal of 83% and 61% was observed at HRTs of 14 and 8.75 days, respectively. Higher color removal (95% and 82%) was found in CZB during both HRTs treatment than C and CZ without

even without zeolite addition. Higher effluent NO3- concentrations were observed in CZB, possibly due to lower bioavailability of organic carbon due to adsorption by biochar. Thus, the recommendation for the design of hybrid sub-surface wetlands is to consider the appropriate and economic organic carbon source addition to anoxic phase as an extra electron donor, which can contribute to higher denitrification performance to the completely remove nitrogen from landfill leachate.

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