Mainstream deammonification at low DO values and employing granular biomass

Marco Salmistraro     TRITA LWR Degree Project Thesis 02:11 
 
 ii 
© Marco Salmistraro 2015 
Environmental Engineering and Sustainable Infrastructure 
Done in association with the Department of Chemical Engineering, University of Barcelona 
Department of Land and Water Resources Engineering 
Royal Institute of Technology (KTH) 
SE-100 44 STOCKHOLM, Sweden 
Reference should be written as: Salmistraro, M (2015) “Mainstream deammonification reac-
tor at low DO values and employing granular biomass” TRITA-LWR Degree Project 
2015:24 47 p.
Deammonification reactor treating mainstream municipal wastewater 
 
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SUMMARY IN ENGLISH  
Water treatment techniques constitute a primarily relevant technical sub-
ject when sustainability is advocated; due to the stringent emergency of 
the topic, dedicated operational choices are required in order to ensure 
maximum efficiency. This thesis focuses on the possibility of reducing 
the incoming nitrogen load of mainstream municipal wastewater through 
naturally occurring biological processes, namely partial nitrification and 
ANAMMOX. Available scientific articles on the topic almost exclusively 
focus on the treatment of wastewater at high temperatures and nitrogen 
loads, as in the case of sidestream effluents; on the contrary, the intent of 
this research was to investigate treatment options for mainstream fluxes, 
notably characterized by lower temperatures, alkalinity reserves, and N 
strength. The whole work started with a thorough literature review: the 
studied process was inserted in a more general framework regarding 
state-of-the-art nitrogen removal techniques. Later on, the attention 
shifted to the experiment, identifying key functional parameters, defining 
them and assigning them optimal value ranges. More specifically, the 
study encompasses the performance of a lab-scale batch reactor, fed with 
an artificially prepared solution; this was modeled on the typical compo-
sition of municipal mainstream water fluxes, as reported in dedicated lit-
erature publications (Mosquera-Corral et al, 2005). Modifications on its 
content were brought sporadically, and with the sole purpose of accom-
modating the evolution in the reactor conditions. The operational choic-
es that were taken included the maintenance of low DO values, ensuring 
appropriate out-selection of nitrite oxidizers (NOB), and the employ-
ment of AOB-enriched granular bacterial culture, both for the partial ni-
trification and for the anaerobic oxidation step. Results showed satisfac-
tory N removal rates, while little quantities of nitrates were observed in 
the system; though turning out successful, the employment of granular 
biomass caused some issues for the biomass retention. Constant moni-
toring of relevant physical and chemical values was carried out, and pro-
vided a solid basis for further analysis. In fact, obtained results were 
studied and compared to presently available data on analogue processes 
for the treatment of different kinds of wastewater. Similarities and diver-
gences were highlighted, and employed as a basis for the formulation of 
suggestions and possible improvements, both on the analytic and the op-
erational side of the project. Particular attention was put to the possibil-
ity of saving organic carbon during the removal of nitrogen for further 
reuse in energy-developing processes, such as anaerobic digestion. Simi-
lar solutions are particularly tempting, as they could represent a first step 
in the direction of energetically auto-sufficient water treatment processes 
(Gao et al, 2014; Jetten et al, 1997).
Deammonification reactor treating mainstream municipal wastewater 
 
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ABSTRACT 
Nitrogen removal from wastewater has been exstensively addressed by scientific litera-
ture in recent years; one of the most widely implemented technologies consists of the 
combination of partial nitritation and anaerobic ammonium oxidation (ANAMMOX). 
Compared to traditional nitrification and denitrification techniques such solution elim-
inates the requirement for an external carbon source and allows for a reduced produc-
tion of excess sludge; furthermore, it brings down the costs associated to aeration by 
60-90% and the emissions of CO 2 by 90%. Similar techniques can turn out to be par-
ticularly interesting when stringent environmental regulations have to be met. 
At present, most of the dedicated research dwells on wastewater at high temperatures, 
high nitrogen loads and low organic content, as it is typical of sidestream effluents; 
this project, instead, is focused on mainstream wastewater, characterized by lower 
temperatures and nitrogen content, but higher COD values.  
At the center of the thesis is the application of a one-stage reactor treating synthetic 
mainstream municipal wastewater. The chosen approach consisted in maintaining low 
DO values, allowing for both for the establishment of a proper reaction environment 
and for the out-selection of nitrite oxidizers; granular biomass was employed for the 
experiment, aiming at effective biomass retention. 
The HRT value was gradually decreased, with a minimum at 6 hours. Resulting nitro-
gen removal rates proved to be satisfactory, with a maximum TN removal efficiency 
of 54%. Retention of biomass was also positively enhanced throughout the experi-
ment, and yielded a final SRT value of 15.6 days. 
The whole process was then inserted into a more complete framework, accounting for 
possible energetic optimizations of similar treatment plants. Employing COD frac-
tionation as a primary step paves the way for anaerobic digestion side processes, 
which can produce methane and ultimately provide energy for the main nitrogen re-
moval step. Therefore, envisioning energy-sufficient water treatment processes seems 
a more and more feasible and realistic possibility. 
 
Keywords: ANAMMOX; Deammonification; Dissolved oxygen control; Granu-
lar biomass; Mainstream municipal wastewater treatment; Partial nitrification. 
1. INTRODUCTION 
The present chapter offers an introductory overview of the relationship 
between the worldwide need for drinkable water and its content in nitro-
gen. The main polluting effects of nitrogenous ions are discussed and in-
serted in the more specific framework of mainstream municipal 
wastewater treatment, highlighting the relevant challenges that this thesis 
intends to face. 
1.1. A global demand for water quality 
The developing increase in global population is intimately intertwined 
with a steady growth of the demand for supporting services, including 
drinking water. On the side, industrial processes and productive sectors, 
ensuring satisfactory life standards for richer countries, also grow in 
number and extend on a bigger and bigger portion of the urban network, 
ultimately contributing to a steady increment in water demand. As a con-
sequence, considerable and augmenting pressure is put on the environ-
ment, and, on a greater scale, on ecosystems. In order for any further de-
velopment to be considered sustainable, the call for efficient, 
economically viable wastewater treatments is stringent. This necessity 
becomes evident when taking into account the consistent increase in
Marco Salmistraro     TRITA LWR Degree Project Thesis 02:11 
 
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population growth, which is likely not to decrease in at least the next 30 
years, (Fig. 1). Alongside population growth, another fact has to be born 
in mind, and is fresh water availability. In spite of the fact that 70% of 
the Earth's surface is made up of water, only a small percentage of it is 
available for human consumption, roughly amounting to 2.5%. Also, 
70% of this fresh water is trapped into glaciers and thus not possibly 
employable; the rest of it lies in groundwater reservoirs or is stored as 
soil moisture. In the end, only the 1% of the global amount of water 
turns out to be available for direct human abstraction and consumption, 
and is the fraction found in lakes, rivers, reservoirs and underground 
cavities that are shallow enough to be tapped at convenient prices. More 
interestingly, this considerably reduced fraction is the only one undergo-
ing natural recharge and thus resulting to be available on a sustainable 
basis (University of Michigan, 2006). Also, the amount of drinking water 
consumed daily, though varying greatly from country to country and de-
pending on the regional socioeconomic conditions, clearly points in the 
direction of an unsustainable development and a flawed water demand 
and supply system. For instance, the average personal daily water con-
sumption in the United States is slightly greater than 550 l/d; this value 
gradually decreases and is assessed at almost 500 l/d for Australia, and 
400 l/d for Italy. The variability of such an important parameter is no-
ticeably wide, as it is clear by considering water consumption levels in 
least developed countries, mainly in the African or South-Eastern Asian 
territories; as an example, personal water consumption in China is lower 
than 100 l/d, and drops down to a few dozen liters in the case of central 
and sub-aharian African countries, like Rwanda, Mozambique or Uganda 
(United Nations Development Program, 2006). Furthermore, other par-
allel mechanisms, such as diffused pollution and contamination, 
Fig. 1. Worldwide population growth and future estimations 
(US Census Bureau, 2015; UN, 2010)
Deammonification reactor treating mainstream municipal wastewater 
 
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Fig. 2. Worldwide water scarcity map (WWAP, 2012) 
 
negatively affect water availability and pose a serious issue when sustain-
ability is among the factors that have to be taken into account.  
A common way to deal with the contemporary issue of insufficient fresh 
water supply is to express it in terms of water scarcity. The United Na-
tions define it as "the point at which the aggregate impact of all users 
impinges on the supply or quality of water under prevailing institutional 
arrangements to the extent that the demand by all sectors, including the 
environment, cannot be satisfied fully" (WWAP, 2012). The definition it-
self of the term implies a high degree of relativity; in fact, scarcity can 
occur both at the level of supply and demand, imply inefficient provision 
patterns, but also inadequate social habits; further variability can be trig-
gered by inhospitable weather conditions, such as severe aridity. As for 
the present day, it has been estimated that 700 million people, spread in 
43 countries, live in water scarcity conditions and it is believed that by 
2025 such number will be more than doubled, reaching 1.8 billion of in-
dividuals (Fig. 2). A relevant distinction has to be made between physical 
and economic water scarcity: while the former term describes the inade-
quacy of a specific ecosystem to provide sufficient water for its function-
ing and self-maintenance, the latter points out the lack of economic 
means for the development of infrastructure and tools for water abstrac-
tion and distribution. The framework that has been designed so far is 
undoubtedly afflicted by heavy unbalances, both at the environmental 
and social levels; therefore, the need for technological advances and 
qualified interventions is clear; moreover, the possibility of developing 
quasi energy-sufficient solutions for water treatment (Jetten et al, 1997; 
Verstraete et al, 2009; Gao et al, 2014) seems to be a viable path for the 
establishment of a more equal worldwide water network, as such tech-
nologies could be easily exported from western, scientifically advanced 
countries and implemented in poorer countries; a favorable point to this 
is also represented by their general economical affordability. Hence, the 
integration of water treatment techniques with other pathways for energy 
recovery is turning out to be a key criterion in the development of new 
facilities and treatment plants. Of course, the implementation of similar 
technologies requires a deep understanding of the pollution mechanisms 
that interest water bodies; knowing what the most frequent contaminants 
are, and being aware of the most common transformations they undergo 
in the ecosystem is a clear prerequisite of functional water treatment 
planning. It is at this stage that environmental engineering comes into 
play, taking up the role of identifying the most critical environmental is-
sues, quantifying them and designing solutions for optimized treatments.
Marco Salmistraro     TRITA LWR Degree Project Thesis 02:11 
 
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1.2. Nitrogen in the ecosystem 
Nitrogen is the most abundant element found in the atmosphere, with a 
volume fraction of about 76%, which roughly corresponds to its molar 
fraction, too. Its natural state is the diatomic form, N 2, corresponding to 
a colorless, tasteless gas, which is also known to be inert. Besides being a 
component of some of the most relevant biochemical molecules, such as 
DNA, proteins and vitamins, it is a fundamental block of some vastly 
widespread inorganic compounds, like ammonia NH 4
+
 and nitric acid 
HNO 3.  More specifically, the former plays a fundamental part in the 
natural chain of reactions involving this element; the role of such bio-
chemical cycle is to manipulate nitrogen and transform it from its inert 
atmospheric form into biologically available compounds. 
A combination of six biochemical reactions constitutes what is regarded 
as a whole closed-ring system (Fig. 3) and normally labeled as Nitrogen 
cycle. 
• Nitrogen fixation This step allows for the conversion of inert, inorganic 
diatomic gas N 2 to an organic, or fixed form. Such process is normally 
carried out by means of microbiological mechanisms; different typolo-
gies of bacteria naturally take up the role of fixing inorganic nitrogen, 
and thus are called nitrogen-fixing microorganisms. Examples of such 
bacteria include Rhizobia, Azotobacteria, Cyanobacteria. Other possibilities 
for nitrogen fixation are represented by high-energy natural events, such 
as forest fires, or man-made reactions; examples of the latter are the use 
of explosives or the combustion of fossil fuels, releasing nitrites and ni-
trates (NO x). 
• Nitrification Aerobic conditions are necessary for nitrifying bacteria in 
order to convert ammonia to nitrites (NO 2
-
) and then to nitrates (NO 3
-
); 
this is a necessary step, as these oxidized forms represent the only way 
for plants and trees to take up nitrogen in their systems. Among nitrify-
ing bacteria the most relevant are Nitrosomonas and Nitrobacteria. 
• Assimilation The transfer of nitrogen-rich compounds, like nitrites, ni-
trates, ammonia and ammonium ions, from the soil matrix to the meta-
bolic system of trees and plants is necessary for the creation of amino ac-
ids, the monomers that ultimately make up proteins. These molecules are 
in fact characterized by the presence of a -NH 2 group linked to their 
main carbon atom. 
• Ammonification (mineralization) Organic forms of nitrogen are converted 
to ammonia-nitrogen. The microorganisms operating such transfor-
mation are also indicated as decomposers, as their task is to break down 
proteins and organic matter found in the soil and turn fixed nitrogen into 
ammonia, which is more frequently identified in the ionic form of am-
monium. The typical substrates employed in this step are dead plants, 
organic matter of animal derivation, and fecal matter. The main bacterial 
types devoted to such function are Bacillus and Clostridium; also, different 
kinds of fungi are known to be involved in the same process. 
• Denitrification Nitrates are converted back to dinitrogen gas. On the 
side, nitrous oxide gas is also produced, but in less noticeable amounts. 
Still, this is a relevant phenomenon, as N 2O is known as a strong green-
house gas. This step runs under anaerobic conditions, and represents a 
natural way of providing a buffer system for excessive nitrogen fixation. 
A potential example of involved microorganism is Thiobacillus Denitrifi-
cans.