Successful start-up of a full-scale wastewater treatment plant (WWTP) is a key issue for the
succeeding operation of WWTP on the one hand and the nutritious phosphorus removal is of
great concern on the other. After the construction of Mudanjiang WWTP with a flow rate of
100,000 m3 d-1 in Heilongjiang Province of China, a novel way of start-up through feeding
wastewater continuously into the system was attempted against the conventional start-up
method of inoculating activated sludge in the aeration tank by feeding wastewater
intermittently. Activated sludge was cultivated and proliferated in the aeration tanks instead of
dosing acclimated sludge from other source. After one-month’s start-up operation, MLSS, SV
and SVI increased to 2.5 kg m-3, 30% and nearly 80% respectively, which indicated that quick
and simple start-up had been achieved. After successful start-up, an investigation into
phosphorus removal was conducted with the emphasis on influencing factors such as ORP
and NOx-N concentration etc. When the aeration tank was switched from aerobic to anaerobic
mode, phosphorus removal efficiency of 80% could be realized within the whole treatment
system. Experimental results revealed that an ORP of -140 mV and NOX-N of 2 mg l-1 were
critical for the anaerobic phosphorus release, and DO in the range of 1.7-2.5 mg l-1, BOD5/TP
of 20-30 and SVI of 70~80 as well as SRT of 5 days were the optimal phosphorus removal
conditions for the aeration tanks.
Biological treatment has been carried out in two different systems: aerated closed and threephase
fluidized bed reactors for hydrocarbons removal from refinery wastewaters. For the two
systems, hydrodynamic study allowed the determination of operating conditions before
treatment experiments. Then, in a second time, biological treatments have been conducted in
the same operating conditions. The obtained results showed that in the three-phase fluidized
bed we can degrade hydrocarbons more rapidly than in a closed aerated bioreactor.
Among the different appropriate techniques available to create efficient contacts between
phases, the three-phase fluidization G/L/S where carrier particles are moving inside the
reactor seems very interesting. It allows an intimate contact between phases and present
many advantages concerning hydrodynamic and mass transfer phenomena. In fact,
depending on operating conditions and the bubble flow behaviour, the three-phase fluidized
bed could display different flow regimes
In these systems called bioreactors the solid particles covered with a biofilm are fluidized by
two ascending flows of air and contaminated water. With favourable operating conditions,
from a hydrodynamic and mass transfer point of view, the pollutant can be biologically
degraded up to 90%.
Until this date, the three-phase bioreactors modelling remains very complex because it
required taking into account several factors: the pollutant biodegradation rate in the biofilm,
the bioreactor hydrodynamic characteristics, and the reactant interfacial gas-liquid and liquidsolid
mass transfer. Thus the essential purpose of modelling is to integrate the microbial
kinetics with the reactor hydrodynamics. We can notice that a few models have incorporated
both bioreactor hydrodynamics and microbial kinetics.
For the steady state bioreactor model, we generally assume that the particles are uniform in
size, the biofilm is uniform in thickness, and the biofilm can be considered as homogeneous
matrix through which oxygen and substrate diffuse and are consumed by the microbes. The
liquid phase in the bioreactor substrate is considered to be axially dispersed while the gas
phase is assumed to be in plug flow . Rittmann (1997) proposed a model based on wake
theory for predicting bed expansion and phase hold-ups for three-phase fluidized bed
bioreactors. In this model he modified the correlation for the computation of the bioparticles
drag coefficient CD . He also attempted to explain the biofilm detachment which can occur
with three broad patterns: erosion, sloughing and scouring and assumed that the factors
affecting detachment rates can be grouped into two categories (physical forces and microorganisms
physiology in the biofilm).
In this study two bench scale activated sludge systems were used, a CSTR and an SBR for
the treatment of coke – oven wastewater. Both reactors were inoculated with activated sludge
from a municipal wastewater treatment plant. At the first stages of operation, reactors were
feed by a mixture of municipal wastewater and synthetic wastewater. Full acclimatization of
the microorganisms to synthetic wastewater was achieved in 60 days. The operation of the
reactors was divided into three distinct periods. The first period was characterized by the
treatment of high organic but non-toxic synthetic wastewater. During this period COD and
BOD5 removal efficiencies reached 95 and 98% respectively, in both reactors. Nutrient
removal was better in the SBR reactor rather than in the CSTR. In the second period phenol
was added in concentrations up to 300 mg l-1. Degradation of phenol started about the 20th
day after its introduction to the reactors. In this period no effects of phenol to nutrient removal
were observed, whereas the removal efficiency of organic matter in both reactors was slightly
decreased. During the third period phenol concentrations of the influent were gradually
increased to 1000 mg l-1, while cyanide and thiocyanite were added to the influent
composition to concentrations reaching concentrations of 20 and 250 mg l-1 respectively. The
composition of the influent of this period was a full assimilation of coke oven wastewater.
Introduction of increased phenol concentrations along with cyanide compounds initiated
irreversible effects on the activated sludge microfauna of the CSTR causing inherent
problems to the treatment process, while SBR showed greater capacity to withstand and
degrade toxic compounds. The beginning of this period was characterized by decreased
settleability of the suspended solids as well as decrease of organic matter and nutrient
removal efficiencies. Monitoring of the effluent characteristics during this period reported over
90% for organic load, 85% of nutrient removal and over 90% of phenol and cyanide removal
in SBR, while the removal efficiencies for the CSTR were 75, 65 and 80% respectively.
Asymmetric multilayer Al2O3 ceramic membranes with pore sizes ranging from 3 to 500 nm
are synthesized in tubular form with external diameter of 14mm, internal diameter of 8mm and
length of 340mm. The membrane synthesis took place on commercially available supports,
with the dip-coating technique either from aloumina particle suspensions or from boehmite
The membranes are subsequently mounted in a pilot-scale module able to accept six
specimens, and used in micro- and ultra- filtration experiments for the purification of aqueous
streams from suspended solids. The experimental module is equipped with a back-flushing
circuit that can be activated on demand to prevent the fouling of the membranes and the
associated reduction in permeability.
For the microfiltration experiments membranes with 100nm pore size are used. In the case of
an aqueous solid suspension with a concentration of 0.1 to 1 wt.% consisting of solid particles
with an average size of 0.5 μm, complete solid rejection is observed. The process has a
capability of treating 0.8 m3 of feed per hour per square meter of membrane surface under an
average pressure difference of 3 x 105 Nt m-2. The fouling of the membranes can be quite
effectively reduced by back flushing at regular time intervals. Under complete retentate
recycling conditions, more than 95% of the feed volume can be recovered as microparticle
For the ultrafiltration experiments membranes with 3 nm pore sizes are used. In the case of
an aqueous solid suspension of nanoparticles with a concentration of 0.1 to 1 wt.% consisting
of solid particles with sizes of 20-30 nm the rejection was also almost complete. The process
has in this case a capability of treating 0.16 m3 of feed per hour per square meter of
membrane surface under an average pressure difference of 3 x 105 Nt m-2. Fouling appears
not to cause serious permeability drop in this case probably because even after the
nanoparticle deposition the membrane hydraulic resistance is the permeability determining
step. Almost the entire feed volume can be recovered as nanoparticle free water under
complete retentate recycling conditions.
Purification experiments are also performed in olive oil mill wastewater. Best results are
achieved by using a two step membrane process with gradually decreasing pore size.
Although complete rejection of solids and significant reduction of the BOD5 and phenol
content of the wastes is achieved, the very low permeability is the main draw back of the
Some amounts of inert products are given into environment due to biological degradation of
substrate in activated sludge system. The effluent of biological wastewater treatment consists
of inert substrate in influent flow, soluble microbial products and non degradable or slowly
degradable organic products.
Soluble inert COD (SI) must be determined for discharge standards since it did not give any
reaction in activated sludge system and was given with wastewater discharge. However
particular inert COD (XI) accumulated in system depending on sludge retention time due to it
is only wasted from system by wasted sludge.
This study focused on inert fractions of Cumhuriyet University campus wastewater which
consists of domestic, hospital and laboratory wastewaters. Experimental method was used
suggested by Orhon et al. and modified by Germirli et al. in order to determine directly influent
particulate and soluble inert fractions. According to the experimental procedure three aerobic
batch reactors, two with the wastewater and the third with glucose were run parallel. In the
reactors, the change in the soluble COD profiles is observed for a period during which all
degradable COD is entirely depleted, in other words, the COD profiles reach a plateau and
Wastewater samples were taken equalization tank in wastewater treatment plant. The
conventional parameters of campus wastewater characterization were as follows: Total COD
(CT0) = 372 mg l-1, total soluble COD (STO) = 124 mg l-1, total suspended solids (TSS) =177
mg l-1, ammonia (NH3) = 31.2 mg l-1, ortho-phosphate (PO4-P) = 11.3 mg l-1 and pH=7,4 .
In this study, in order to determine inert COD fractions in Cumhuriyet University campus
wastewater, three aerobic batch reactor systems were used. At the end of approximately 381
h operation, COD composition of campus wastewater were found to be CT0=372 mg l-1,
XS0=56 mg l-1, SS0=104 mg l-1, CS0=149 mg l-1, SI=12 mg l-1, XI=211 mg l-1, respectively.
This paper presents a biological method for controlling odor problems caused by H2S
originating from sewer networks under anaerobic conditions. The proposed method is based
on the continuous addition of nitrate which oxidizes dissolved sulphide according to an
autotrophic biological procedure and inhibits further sulphide production by sulphate reducing
bacteria, until complete denitrification.
The proposed method was first tested at laboratory in a 3 l anaerobic batch reactor simulating
municipal wastewater of the city of Corfu in respect to sulphate concentration. Addition of
nitrate in non-septic (not sulphide containing) wastewater inhibits the production of sulphide
until complete denitrification. Heterotrophic denitrification rate was found 4.5 and 3.9 mg NO3-
N l-1 h-1 at 250C and 300C respectively. Higher C/N ratio is, probably, responsible for the
increased denitrification rate of the lower temperature.
Interestingly, addition of nitrate in a septic wastewater led to a preferential autotrophic
denitrification with sulphide as electron donor at a rate of 0.8 and 1.5 mg NO3-N l-1 h-1 at 25
and 300C. After complete sulphide oxidation, heterotrophic denitrification takes place inhibiting
any further sulfate reducing activity.
The effectiveness of the method was validated by field experiments in a 6.7 Km combined
sewer network in the city of Corfu, with an average wastewater flow of 500 m3 h-1, an average
retention time of 2 h and sulphide concentrations varying from 3 to 27 mg S2- l-1. Continuous
addition of 6.9, 15 and 27.7 Kg NH4NO3 h-1 for a period of 4 to 8 hours led to an average
sulphide removal efficiency of 84%, 98% and 99%, respectively.
Based on these experimental results, a continuous addition of 10 Kg NH4NO3 h-1 is proposed
for practical implementation as the optimal dosing, considering sufficient odor control and
tolerable increase of the ammonia load. The proposed method is not only effective but also
financially interesting taking into account the facility cost and the monthly operational cost,
during the summer months of the year.
The process of nitrification in wastewater treatment is widely accepted as a two-step process. In
the first step the ammonia is oxidized to nitrite, a process considered to be carried out mainly by
the Nitrosomonas sp., while in the second step the Nitrobacter sp. oxidizes the nitrite to nitrate.
Both species are autotrophic (chemolithotrophic) and they use CO2 as the only carbon source for
growth and maintenance, as well as, inorganic reduced nitrogen compounds to satisfy their basic
needs for energy.
In the present work, experiments were carried out in a chemostate reactor, using a specific
synthetic medium, in order to study the kinetic characteristics of nitrifying pure cultures. In the first
set of experiments, the nitrosifying bacteria Ns. europaea were used, while in the second set we
employed the nitrifying bacteria Nb. winogradkyi. Subsequently, a specially prepared mixed
culture, consisting of the two above mentioned species was studied, in order to evaluate the
possible interactions between them.
In order to determine the influence of the pH on the growth rate of pure cultures and to determine
the optimum pH value, a series of chemostate experiments was conducted with gradual changes
of the pH. The optimum pH was determined at 7.5-7.6.
The nitrosifying bacteria oxidize ammonia to nitrous acid, whereas the nitrifying bacteria oxidize
nitrous acid to nitrate. Their growth rate and kinetic behavior depend on the concentration of the
energy source and also on the concentration of the dissolved oxygen and CO2. Therefore, the
kinetics can be described by means of the Monod equation.
The half-saturation coefficient for the energy source was determined by non-linear regression of
the steady state data, which provided the corresponding values of Κm,NH3 = 0.62 mg ΝH3 l-1 and
Κm,HNO2 = 21.8 μg HΝO2 l-1 for each pure culture, on the actual substrates for the specific species.
The influence of the dissolved oxygen concentration on the microbial activity was studied under
controlled conditions in the chemostate, i.e. pH=7.6, T=30°C and HRT=14 h. The results for
several steady state conditions and for different dissolved oxygen concentrations provided the
value Km,O2 = 0.408 mg O2 l-1 for Ns. europaea. Under similar conditions for the culture of Nb. winogradskyi, altering only the retention time in the chemostate i.e. pH=7.6, T=30°C and HRT=28
h, the results provided the value Km,O2 = 1.657 mg O2 l-1.
The influence of the CO2 concentration and its limiting role on the bacterial growth was also
investigated, under steady state conditions, as it is important for the synthesis of new cells by the
autotrophic bacteria. The values of Km,CO2 for Ns. europaea and Nb. winogradskyi were calculated
to 3.8μmol l-1 and 0.37μmol l-1 respectively, which indicates that the substrate affinity for the Ns.
europaea is higher by one order of magnitude than the one for the Nb. winogradskyi.
This paper aims at a comparative evaluation of the total cost of urban sewage processing
units for several treatment systems, appropriate mainly for small capacity plants. The studied
systems are: Oxidation Ditch (O.D.), Trickling Filter (T.F.), Rotating Biological Contactor
(R.B.C.), Compact Sequential Batch Reactor (S.B.R.), Waste Stabilization Ponds (S.P.) and
Subsurface Constructed Wetland Systems (C.W).
For each system, operation and construction costs are calculated as a unit capacity function
for a 40-year operating period. Cost calculation is based on the analysis of its several
components such as energy consumption, chemicals consumption, personnel salaries,
maintenance expenses, construction materials and their respective quantities, required
mechanical equipment and land value. All pecuniary flows, in order to be comparable are
converted into current value.
Cost estimation is based, mainly, on the calculation of the several cost elements’ quantities,
with the development of standardized plans. Total and partial costs are expressed as
functions of plant capacity. The annual operation and maintenance (O&M) cost, the project
cost, as well as the total construction, maintenance and operation cost for 40 years of
operation (Present Value) can be written as a function of flow rate, in the form of a+bQ+cQ2;
whereas energy cost can be described by a linear function of flow rate, in the form of a+bQ,
with excellent approximation. The coefficients a, b, c, for the various treatment methods
examined and for every cost category are summarized in tables.
All treatment methods exhibited positive scale economies for the studied region of cost per
E.P.; this trend was especially evident for plant capacities up to 5,000 E.P.
Natural wastewater treatment methods present the least expensive option for the examined
range of E.P. The classification of the treatment methods from the least to the most expensive
one depends on plant capacity. The classification of the treatment methods based on their
cost for different plant capacities is provided.
The results provide a first level of information, which could be utilized for a quick financial
evaluation of the aforementioned systems as well as in the general decision making plan.
The methylation of mercury has been investigated and documented mainly in sediments, fish
and microorganisms, while limited number of relevant studies is available for wastewater. The
procedure of mercury methylation can occur via biological pathway (by microorganisms) and
via chemical or photochemical reactions.
Methylation of mercury occurs mainly under anaerobic conditions, but some studies have
shown its existence also under aerobic conditions. The resulting concentration of methyl
mercury, which is a highly toxic compound, depends on the specific rates of
methylation/demethylation of mercury. The factors affecting these procedures are the
availability of inorganic mercury, pH, organic matter concentration, microbial activity, redox
potential and temperature. Bacteria which can methylate mercury are often present in
wastewater, and, therefore, the formation of methyl mercury during wastewater treatment is
The objective of the present investigation was the determination of methyl mercury in a pilotscale
activated sludge wastewater treatment plant supplied with synthetic wastewater
enriched with mercury. For this purpose, a Liquid-Liquid Extraction / Simultaneous
Derivatization - GC/MS method was developed and applied for the analysis of samples from
the aeration tank, from the treatment plant effluent and from the sludge.
Methyl mercury was not detected in the samples (detection limit 0.07 μg l-1), leading to the
conclusion that mercury is not methylated under the particular experimental conditions of the
pilot-scale water treatment plant.
Kinetics for the biological processes of nitrification, denitrification and carbon oxidation were
studied in the aerobic and anoxic phases of a pilot scale Biological Nutrient Removal (BNR)
plant treating municipal wastewater. The configuration of the treating system is based on the
combination of the UCT (University of Cape Town) design and the step feeding process in a
In order to study the process kinetics and to obtain reliable values for the investigated kinetic
parameters batch experiments were performed. For this purpose, continuous feeding of the
treating system was interrupted for a given period of time and the pilot plant was turned into a
batch mode of operation. Thereafter, addition of NO3
--N and NH4
+-N into the anoxic and
aerobic compartments of the treating plant, respectively, followed, whereas adequate initial
concentration of a carbon source (municipal wastewater or synthetic substrate) was ensured
in the mixed liquor. Experimental data indicated that the examined biological processes
followed saturation kinetics.
The maximum specific denitrification rate, qDN,max , was found to obtain values, depending on
the type of the carbon source, between 0,045 and 0,390 gNO3
--N/(gXHET·d), whereas the
extremely low value of the half saturation constant for the denitrification process (Km,NO3-N <<
1mgN/l) indicated its description by zero order kinetics. The maximum specific nitrification
rate, qN,max, was determined to vary in a narrow frame, between 1,28 and 1,60 gNH4
N/(gXAO·d). The half saturation constant for the nitrification process, Km,NH4-N, was estimated
graphically at 3,1 – 6,1 gNH4
+-N l-1, corresponding to 62 – 122 μgNH3-N l-1. These values are
considered to be in good agreement with the literature.
The determination of kinetic parameters can be considered as a useful tool for the process
design, operation and improvement of wastewater treatment plants. Furthermore, the study of
the biological process kinetics contributes to the better understanding and outline of the
complicated biological processes that contemporarily take place within the various phases of
BNR wastewater treatment plants.