Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Sarina J. Ergas, Ph.D.

Committee Member

Qiong Zhang, Ph.D.

Committee Member

John Kuhn, Ph.D.

Committee Member

Kathleen Scott, Ph.D.

Committee Member

Peter van der Steen, Ph.D.

Keywords

anaerobic digestion centrate, biological nitrogen removal, bioregeneration, clinoptilolite, photobioreactor

Abstract

Nitrogen pollution has been considered one of the major problems of the 21st century. Discharge of nitrogen from improperly treated wastewaters into surface water bodies causes eutrophication and hypoxia, which results in significant environmental, public health and economic damages. In addition to the incoming flow, wastewater treatment plants generate internal highly concentrated ammonium streams, such as anaerobic digestion sidestream. As a current practice, sidestream without prior treatment is returned to the head of the plant, which increases the total incoming nitrogen load by 20-30% and often exceeds the treatment capacity. The most commonly used conventional biological nitrogen removal processes are energy and chemically intensive. Aging infrastructure and lack of land for plant expansion call for the development of alternative cost-effective treatment technologies. This dissertation investigates novel algal-bacterial technologies to reduce the concentration of ammonium in the sidestream. Applications of algal-bacterial consortia, where algae produce oxygen during photosynthesis replacing mechanical aeration, can significantly reduce the cost of treatment.

Algal-bacterial photosequencing batch reactors (PSBRs) have been developed that promote shortcut nitrogen removal for treatment of high ammonia strength wastewaters. However, the effect of solids retention time (SRT) on nitrogen transformations and microbial communities in PSBRs had not been previously explored. Bench-scale PSBRs with algal-bacterial biomass were operated at SRTs of 5, 10, and 15 days, with alternate light and dark periods, to treat anaerobic digestion sidestream. The sidestream contained elevated concentrations of phosphorus from the digestion of polyphosphate accumulating microorganisms present in waste activated sludge. Therefore, excess phosphorus was precipitated in the form of struvite prior to feeding the PSBRs. High concentrations of ammonium in the influent and low dissolved oxygen concentrations produced by algae during photosynthesis promoted the out-selection of nitrite oxidizing bacteria. The shortest SRT (5 days) resulted in an unstable algal-bacterial community characterized by frequent biomass washout. The average ammonium removal efficiency was 84% for the 5 day SRT and 92% for SRTs of 10 and 15 days. The main nitrogen removal mechanisms were nitritation/denitritation followed by biomass assimilation and ammonia volatilization.

Nitrogen removal from anaerobic digestion sidestream is quite challenging due to high free ammonia (FA) inhibition for microorganisms. Natural zeolites such as clinoptilolite can alleviate FA inhibition by temporarily adsorbing ammonium. Considering the elevated temperature of a sidestream and the presence of other cations, which can compete with ammonium ions for adsorption sites, the effect of both temperature (21ºC and 35ºC) and competing cations on ammonium adsorption capacity of clinoptilolite was investigated. An increase in temperature was not found to significantly affect ammonium removal efficiency and maximum adsorption capacity of clinoptilolite. Langmuir, Freundlich and Langmuir IX isotherm models all provided a good fit to the experimental data (R2>0.98). The presence of competing cations did not significantly impact ammonium adsorption kinetics. A pseudo second-order kinetic model provided a good fit to the kinetic data (R2>0.98). A dosage needed to reduce FA inhibition to AOM, anammox and algae can be calculated using a Langmuir model.

Zeolite that is saturated with ammonium can be biologically regenerated using ammonia oxidizing microrganisms growing as biofilm on its surface. The zeolite can then be reused in subsequent cycles. In this research, zeolite bioregeneration was carried out using two different anammox inocula: anammox granules and enriched waste activated sludge, present in suspension or in biofilm. Additionally, the effect of zeolite on anammox activity was investigated. The results showed similar microbial activity for microcosms inoculated with anammox granules and waste activated sludge. The results indicate that anammox can be successfully enriched from waste activated sludge. Although no statistically significant difference in nitrite removal rates was observed in microcosms with or without zeolite, anammox were able to successfully bioregenerate clinoptilolite and improve its adsorption capacity.

Due to their high ammonium adsorption capacity, the addition of zeolite to a reactor can reduce FA inhibition to microorganisms and improve nitrogen removal efficiency. In this research, clinoptilolite was added to a PSBR inoculated with anammox and operated with alternating light and dark periods. The experiment consisted of three phases. During phase 1, a PSBR with anammox treating diluted high ammonia strength wastewater with an average concentration of 500 mgN/L was operated to investigate the feasibility of partial nitritation anammox process in a PSBR. Once the process was established, zeolite was gradually added to the PSBR, resulting in increased nitrite production rates during the light period. During phase 3, the ammonium concentration in the influent was increased to 1,841 mgN/L to mimic high ammonia strength wastewater and a higher zeolite dosage was added based on the isotherm studies. The results showed that zeolite addition could alleviate free ammonia inhibition for AOM, anammox and algae and improve nitrite removal rates. Despite low aqueous ammonium concentrations, increased nitrite removal rates were observed, which indicated bioregeneration. An overall TN removal efficiency of >90% was observed after 9 days of reactor operation.

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