Biological method of treating wastewater in batch with porous biomass carrier

An improvement in the biological method for treating wastewater is provided. The method is featured by adding to the reactor an amount of floating porous biomass carrier which can be mixed thoroughly with the wastewater to be treated. By the utilization of the carrier, the microorganisms can be retained in the reactor in a high concentration and the mass transfer can be adjusted so that various phases of microorganisms are provided within the reactor. The method is also characterized in that the reactor is operated under aerobic, anoxic and/or anaerobic conditions which are sequentially provided in an appropriate order depending on the type of pollutant to be treated. The method can remove organic substances, and nitrous and phosphorus materials effectively in a single reactor, and reduce the volume of the resultant sludge and the capital investment greatly as compared with the prior art methods.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improvement in a biological method of 
treating wastewater. More particularly, the present invention relates to a 
biological method of removing dissolved organic substances, and nitrous 
and phosphorus materials present in wastewater efficiently in a batch 
reactor containing porous biomass carriers. 
2. Description of the Prior Art 
In general, wastewater includes organic substances, nitrous and phosphorus 
materials, and the like, which serves as a nutrient source necessary for 
certain microorganisms to carry out their metabolism. The methods 
utilizing this type of biological function of the microorganisms in the 
field of wastewater treatment are called "biological methods for treatment 
of wastewater." 
Conventionally, the methods involving the treatment of wastewater comprises 
transferring pollutants such as organic substances, and nitrous and 
phosphorous materials into microcells or converting these pollutants into 
environmentally innoxious form through a biological reaction, and 
separating the resultant microbes and innoxious product from the 
wastewater for disposal. 
A wide variety of microorganisms and environmental conditions can be 
utilized depending on the type of the pollutant to be treated. For 
example, organic substances are converted into carbon dioxide and water by 
the action of heterotrophic microorganisms intaking such organic 
substances as a carbon source under aerobic conditions, and into methane, 
carbon dioxide, hydrogen, water, etc., under anaerobic conditions. 
Nitrogen is converted into oxidative nitrogen such as nitrite or nitrate 
by nitrifying bacteria under aerobic conditions. However, under anoxic 
conditions (i.e., under dissolved oxygen free conditions), nitrogen is 
converted into an innoxious form such as nitrogen or nitric acid gas 
through a denitrification reaction by the action of heterotrophic 
microorganisms. Phosphorus is uptaken in the form of a dissolved 
phosphorus by a bacteria having phosphorus accumulating capacity, and 
accumulated therein in the form of granules under an aerobic conditions. 
However, the phosphorus granule thus accumulated are released from the 
microorganisms in the form of a dissolved phosphorous under anaerobic 
condition (i.e., under dissolved oxygen and nitric acid free conditions). 
In order to maximize the efficiency of the biological treatment of 
wastewater, it is necessary to choose proper microbes depending on the 
type of pollutant to be treated and provide suitable environmental 
conditions for growth to enhance the microbial activity, as well as 
increasement in the amount of microorganisms within the reactor. 
Several methods have been hitherto proposed in attempt to enhance the 
activity of microorganisms used. According to one of these methods, the 
reactor is partitioned spatially so as to provide efficient conditions for 
the growth of the microorganisms. However, this method has drawbacks that 
it requires broad spaces of the treatment facilities and, therefore, 
enormous capital investment for constructing the treatment facilities. 
Furthermore, the method suffers from the defects that the manipulation of 
treatment facilities is grossly complicated. 
As an improvement of this method, it has been proposed to increase the 
concentration of microorganisms by recycling the produced microorganisms 
or adding a biomass carrier to the partitioned reactor. This improved 
method could reduce the required treatment facilities spaces to some 
extent. However, it still requires broad spaces for treatment facilities, 
resulting in higher capital investment. 
Another approach was a slurry type treatment method using a batch reactor, 
in which the reaction conditions are changed with the lapse of time by 
controlling the amount of dissolved oxygen. However, this method could not 
increase the concentration of microorganisms to above 5,000 mg/L because 
the sedimentation for separating the resultant sludge from the treated 
wastewater must also be carried out in the same reactor. Thus, this method 
is not suitable for treating a large volume of wastewater. 
In addition, separation of the surplus sludge from the treated wastewater 
has been carried out mainly by a gravitational sedimentation method or a 
floatation method. However, the resultant sludge has a low concentration 
and, thus, this type of separation method must be accompanied by 
expensive, additional treatment procedures in order to attain the 
resultant sludge in a high concentration. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an improved biological method of 
treating wastewater in which pollutants such as organic substances, and 
nitrous and phosphorus materials contained in the wastewater can be 
effectively removed in a single reactor. 
Another object of the invention is to provide an improved biological method 
of treating wastewater which can maximize the activity of microorganisms 
used, thereby the size of the equipment for wastewater treatment being 
reduced greatly and the treatment procedures being simplified. 
Yet another object of the invention is to provide an improved biological 
method for treating wastewater which produces sludges in a high 
concentration, and thus which is suitable for the treatment of a large 
volume of wastewater and can reduce the cost for the subsequent treatment 
of sludges. 
A further object of the invention will become apparent through reading the 
remainder of the specification. 
These and other object of the invention can be achieved by the method 
according to the present invention, wherein an amount of floating porous 
biomass carrier is added to a batch reactor so that microorganisms are 
retained in a high concentration and aerobic, anoxic and/or anaerobic 
conditions are provided within the reactor in an appropriate order 
depending on the type of pollutant to be treated. 
According to the present invention, the floating porous biomass carrier 
which can be mixed thoroughly with wastewater is added to a batch reactor. 
This type of floating porous biomass carrier can render the microorganisms 
retained in a high concentration and enhance the efficiency of mass 
transfer without being affected greatly by the increasement of shear 
stress of the fluid within the reactor. 
The biomass carrier according to the present invention should not be 
decomposed by the microorganisms used and has a sufficient durability to 
use it repeatedly after removing the sludge. The biomass carrier may be in 
the form of a cube having a side length of 0.5 to 2.0 cm or in the form of 
a corresponding sphere. The microorganism carrier has a density of 
0.1-1.0, a porosity of 40-98% and a pore diameter of 10-3,000 .mu.m. The 
biomass carrier is usually produced from polymeric materials. Other 
materials having adsorbability or ion exchange capacity can be mixed with 
the polymeric materials depending on the type of pollutant to be treated. 
The biomass carrier according to the present invention restricts the 
transfer of materials such as oxygen, resulting in various microbial 
phases. For example, even under an aerobic condition, the interior of the 
biomass carrier can remain in an anoxic or alkaline state. Attributing to 
this property, the time required for the subsequent treatment can greatly 
be reduced. 
The biomass carrier according to the present invention may be added to the 
reactor in an amount of 5 to 40% by volume, preferably 10-30% by volume 
based on the volume of the reactor, depending on the type of pollutant to 
be treated.

DETAILED DESCRIPTION OF THE INVENTION 
An embodiment of the prior art biological method using a conventional batch 
reactor is illustrated in FIG. 1. 
The prior art method comprises the following steps a) to f), as 
diagramatically shown in FIG. 1. Wastewater 2 to be treated is introduced 
into a reactor 1 (Step a). The wastewater and microorganisms are mixed 
thoroughly by an aid of air 3 blown into the reactor from the bottom by an 
air pump 4, and then subject to a biological reaction (Step b). The 
resultant mixture is separated into two layers by sedimentation (Step c). 
After the separation, the supernatant wastewater 6 is drained from the 
reactor (Step d). Then, a portion of the sludge 1 which remains as the 
lower layer is removed form the reactor (Step e). Upon completion of 
removing the sludge, the reactor is allowed to stand until a fresh 
wastewater is introduced for the next run. 
The biological method for treating wastewater according to the present 
invention is an improvement in the above prior art method and illustrated 
in FIG. 2. 
The method according to the invention comprises the steps of: 
a) introducing wastewater, together with an amount of floating porous 
biomass carrier, into a batch reactor containing microorganisms, thereby 
the microorganisms being retained in a high concentration; 
b) mixing and biologically reacting the wastewater with the microorganisms 
under aerobic, anoxic and/or anaerobic conditions which are sequentially 
provided in an appropriate order depending on the type of pollutant to be 
treated; 
c) separating the resultant mixture into two phases by means of 
sedimentation; 
d) draining the supernatant wastewater from the reactor; 
e) removing a portion of the sludge which remains as the lower layer from 
the reactor; and 
f) allowing the reactor to stand until a fresh wastewater is introduced for 
the next run. 
According to the invention, a porous biomass carrier 12 is added to a 
reactor 1 in an appropriate amount in view of the purpose of treatment, 
and then wastewater 8 to be treated is introduced into the reactor (Step 
a). 
Then, while aerobic conditions (Step b") and anoxic or anaerobic conditions 
(Step b') are sequentially provided within the reactor 1 in an appropriate 
order depending on the type of pollutant to be treated, the wastewater and 
the microorganisms are mixed and subject to a biological reaction. A water 
pump 9 is used to provide anoxic or anaerobic conditions within the 
reactor. Aerobic conditions can be provided by means of an aerator 10 
alone or together with a water pump. 
The aerator 10 used should be powerful enough to mix the contents of the 
reactor 1 thoroughly and supply a required amount of oxygen. When using a 
micro-aerator with a high oxygen efficiency as the aerator 10, a recycling 
pump 11 should also be used. A carrier protector (not depicted in the 
drawing) may be preferably installed to the inner side of the reactor so 
that the pump is not impaired. In addition, it is preferred to provide a 
lining to the inside of the reactor in order to prevent the reactor from 
abrasion. 
The resultant mixture is then subject to sedimentation (Step c). In this 
step, while the operation of aerator 10 and/or the water pump is stopped 
(i.e., stagnation state), the microorganisms which are floating or 
attached to the carrier are separated from the treated wastewater by means 
of gravitational sedimentation. After phase separation, an amount of the 
supernatant wastewater 13 is removed through a movable drain tube 16 
positioned at the upper portion of the reactor (Step d). The amount of 
wastewater removed is preferably within the range of 30-80% based on the 
amount of wastewater introduced. 
The sludge and carrier retained in the reactor as the lower layer are then 
removed from the reactor, thereby the amount of the microorganisms within 
the reactor being adjusted to an appropriate level (Step e). The sludge 
and the carrier thus removed are then transferred to a sludge treating 
equipment 15 as depicted in FIG. 3. In this equipment, carrier 17 in 
admixture with sludge is passed through a gauge belt 18 where the carrier 
is separated and sludge 20 is concentrated. The carrier 19 thus separated 
is recycled to the reactor. The sludge separated in the equipment 
undergoes the conventional procedures for sludge treatment. 
After the removal of sludge and before the introduction of fresh wastewater 
for the next run, the reactor is allowed to stand (Step f). During this 
time period, the reactor 1 may be either in a stagnation state or operated 
in the same manner as in Step (b') and/or Step (b"). 
As described hereinabove, the biological method of treating wastewater 
according to the invention is featured by the addition of an amount of 
floating porous biomass carrier which can be mixed thoroughly with 
wastewater to a batch reactor. By making use of the carrier according to 
the invention, the concentration of the microorganisms within the reactor 
can be increased to above 10,000 mg/L and the mass transfer can be 
adjusted so that various phases of microorganisms may be provided within 
the reactor. 
Another feature of the method according to the present invention is that 
aerobic, anoxic and/or anaerobic conditions are sequentially provided 
within the reactor in an appropriate order so as to ensure efficient 
removal of the organic substances, and nitrous and phosphorus materials. 
In addition, since the sludge resulted from the method according to the 
present invention has a high concentration, the expense for conducting the 
subsequent sludge treatment can be reduced greatly. 
Further, the method according to the present invention can be carried out 
in a small reactor, resulting in less capital investment.