|
|
Environmental protection is a basic national
policy of China, and the protection for water resources is especially
onerous. Technicians have been exploring new water treatment technologies
that are practicable in China in the extensive water treatment field
from mid 1980s.
Hydrolization-aerobic technology (H/O process) is a new technology
for organic wastewater treatment developed by Shanghai Jinshan Combined
Environmental Engineering Co., Ltd. It is a mature technique with
8 years in engineering practice. This discourse gives an overview
to the process.
1. Hydrolization Principles
 Biochemical
techniques are most used in organic wastewater treatment, and hydrolization
is a newly developed process, by which complex organic molecules are
degraded into simple compound when reacted with hydrolases in presence
of water molecules. The efficiency of enzyme-catalyzed reaction is
106－1013 times that of non-enzyme-catalyzed
reaction. The reaction takes place under anaerobic conditions.
▲How to distinguish between hydrolization and anaerobic processes?
An anaerobic reaction falls into 4 phases: hydrolization, acidification,
acidity decline, and methanation. During the hydrolization phase,
solid substances are converted into soluble, large molecules into
small molecules, and un-biodegradable substances into biodegradable
substances. During the acidification phase, various organic substances
are degraded into organic acids. As hydrolization and acidification
goes rather swiftly, it is hard to make a clear cut line between them.
The main microbes involved are bacteria hydrolysate and acid-generating
bacteria.
The hydrolization process as referred is to utilize the first 2
phases of the anaerobic process without entering the third phase.
In order to distinguish the method from the anaerobic process, the
method is named as hydrolization process. Although it is named “hydrolization”
process for short, it consists of the two phases, hydrolization and
acidification.
The hydrolization process involves mainly facultative microbes,
which are of large numbers in natural environments, and multiply fast.
While the methane-generating bacteria in the anaerobic process in
are obligate anaerobes, which are more sensitive than facultative
microbes to surroundings, such as changes in pH value, alkalinity,
heavy metal ions, detergent, ammonia, sulfide, temperature with a
much longer reproduction cycles (long generation time).
The most eminent difference between the 2 processes lies in that
the hydrolization takes place under anoxic conditions, while the anaerobic
process is under anaerobic conditions. The term, anaerobic, refers
to absolute non-presence of oxygen (DO=0), whereas anoxic refers to
a condition where DO<0.3－0.5mg/l.
Since the hydrolization process takes place under anoxic conditions,
in practice, the aerobic process may proceed after the hydrolization
process in a same reactor of the hydrolization process. In order to
differentiate from the anaerobic- aerobic process, the hydrolization
and anoxic technique is named as H/O process for now.
2. Characteristics of Hydrolization Process
① The ratio of BOD5/CODCr of wastewater
increases remarkably after the hydrolization process.
② Compared to the anaerobic process, hydraulic retention time
for the hydrolization process is shorter, as the reaction typically
finishes in 4~18 hours.
③Featuring a large number of microbes and large volume load, the
membrane hydrolization process is able to accommodate load variation
of inflow CODCr, i.e. the higher the inflow concentration,
the higher the removal efficiency of CODCr will be.
 ④The
hydrolization process is more stable and less affected by outside
temperature changes. Typically, the water temperature is between 5~40℃,
due to the synergism between mesophilic bacteria and the psychrotrophic
bacteria.
⑤ The hydrolization tank gives no odor as that of the anaerobic
process does. The deeper the tank is, the higher the efficiency will
be. As the depth of tank may go down to 8.5~9m, land can be saved.
⑥Hydrolization bacteria are facultative microbes, which are different
from the methane generating bacteria in the anaerobic process. The
methane generating bacteria are obligate anaerobes, which die if substrate
substances change. Hydrolization bacteria multiply fast, and are highly
adaptable to surroundings. Thus the hydrolization process is given
an edge over the anaerobic process, and it can accommodate differently-structured
products.
⑦CODCr increases along with the time. Take, wastewater
treatment station of Ginsber Beer In Siping (Jiling Province, China),
for example, the removal rate of the station is 50% at the time of
inspection and acceptance, and the figure is increased to 80% in June
1998.
⑧The multi-phased H/O process can realize bio-denitrogenation. Engineering
practice has demonstrated that ammonia nitrogen in untreated water
of 299mg/l may drop to 15%mg/l.
⑨Typically, treatment stations are built with regulation tanks.
In practice, the regulation tanks can be used as membrane hydrolization
tanks when supplemented with portioning and fiber fillers. Thus investment
on infrastructure can be saved. As hydrolization tanks are of high
CODCr removal rate, they can be used as structure level
for CODCr removal. If the regulation tanks of an existing
wastewater treatment station are converted into hydrolization tanks,
the elimination rate for CODCr can be boosted by 30%.
3. Performance Index of Hydrolization Process
The removal rate of CODCr in hydrolization tank is 30-50%
(60-80% in certain cases);
The hydrolization rate of suspended solid substances is 50-65%;
Hydrolization-aerobic process can save about 40% of energy comparing
with all-aerobic process;
Saving for 20-30% land as may be required by the anaerobic or all-aerobic
process; and The total removal rate of CODCr of Hydrolization-
aerobic treatment (H/O treatment) can be 95-98%.
4. Application of Hydrolization Process
1、 Organic substances
① Biodegradable organic pollutants of large molecular weights,
such as polysaccharides substances (starch), are hydrolizated into
monosaccharide (dextrose) or organic acids, the protein into amino
acids, and the fat into fatty acids and glycerin.
② Nitrobenzene is hard to degrade. But under anaerobic conditions,
it can be converted into aniline, and further be completely degraded
through aerobic biochemical reactions.
③ Hydrolization damages the chromophoric gene of dyestuff,
such as azo dyestuff (with chromophoric gene being -N=N-).
④The hydrolization of phenol causes the breaking of cyclic molecule
linkage.
⑤Hydrolization accelerates the breaking of PVA molecule linkage
of chemical slurry for printing and dyeing.
2、Treatable industrial wastewater
The hydrolization process has been adopted in treatment of industrial
wastewater from: food plants, beer brewing, fermentation and brewage,
bio-pharmacy and synthesis pharmacy, tanning, petrochemicals, special
chemicals, chemical dyestuff, and textile printing and dyeing.
3、Applicable CODCr concentration range
The industrialized hydrolization process at present is capable of
wastewater treatment with CODCr inflow concentration of
10000-15000mg/l, i.e. high-concentration organic wastewater treatment. |
|
