Монгол улсад үйл ажиллагаа явуулж буй бохир ус цэвэрлэх байгууламжуудын хүчин чадлыг нэмэгдүүлэх, шинээр цэвэрлэх байгууламж барих ажил чухал шаардлагатай байгаа бол хамгийн чухал зүйл нь цэвэрлэгээний технологийн шинэчлэл юм. Та бүхэнд Швед улсын Амьдралын шинжлэх ухааны их сургуулийн "Swedish university of life science" мастер оюутны эрдэм шинжилгээний өгүүллийг хүргэж байна.
Special
thanks to Matthew Riddle
in
recognition of the support
from my
friend Robin Hagblom
Phosphorus removal cycle in wastewater
treatment process – a Mongolian perspective
GUYEN Battuvshin, Warsaw
University of Life Sciences, Student of the Environmental Engineering –Environmental
Protection – Master’s Programme
Introduction
Phosphorus
is an essential element in the world. The symbol for phosphorus is P. It is a
nonmetallic chemical element and atomic number 15. The name of phosphorus name
given from Greek mythology Φωσφόρος
which it means light bearer also in Latin ”lucifer”. Phosphorus removal in wastewater
treatment is crucial because high
nutrients concentration leads to eutrophication and reserves of phosphorus are
decreasing. Modern developed countries have developed phosphorus removal
strategy used in wastewater treatment plants. Mongolia also understand concept
of removing phosphorus from wastewater is important to prevent future
environmental changes and try to follow developed countries. The only Mongolian
wastewater treatment plant was built in 1964. Until today, Mongolian wastewater
treatment plant operates only in basic level removing from organic pollutants.
The treatments need to be improved because of downstream pollution. This paper
aims explore which method of phosphorus removal is more suitable for Mongolian
environmental conditions.
This project paper will review both literature
concerning Phosphorus removal.
The main sources for the literature search will be the database of SLU
library and Google-scholar.
Methods of phosphorus removal in wastewater treatment
process
Mongolian
wastewater treatment plant treats the water in two steps: Mechanical and
biological. Mechanical treatment system includes four stages. A pump station where
industry, farm or city wastewater is directly gathered in pump station location.
Sand filter is used to filter pump station water. Sedimentation process is the
removal of particulate matter, chemical floc, precipitates from suspension
through gravity settling. During sedimentation process manure is extracted from water but not fully.
The sludge continues to the sludge digestor where it is dried. The
product of sludge digesting stage I treated manure which is left in open space.
The biological treatment system treats the water from sedimentation process
biologically and also includes few important steps for treating water after
mechanical treatment. After sedimentation process, aeration process exposes the
wastewater to air because biological treatment process requires aeration. The
secondary sedimentation is next and is a
similar process to the previous mechanical sedimentation process. The secondary
sedimentation process extracts most of the remaining sludge from the water. The
activated sludge process removes any remaining sludge with by microorganisms. This
sludge is sent The last stage is disinfection
of the water with ultra violet light to kill microorganisms from activated
sludge process or somewhere else.
Applicability
of different phosphorus removal methods in Mongolia
Most
wastewater treatment plants in the world
use chemical processes to remove P but modern developed countries aim to
increase the number of treatment plants using biological phosphorus removal. Biological
phosphorus is the phosphorus included into the biomass for cell growth and
orthophosphates and polyphosphate result from the decomposition of organic
matter and can be removed through biological and chemical phosphorus removal
processes. The mechanical and biological wastewater treatment strategy stages
are crucial but must be adapted to Mongolian harsh climate which make the
biology stages inefficient. The
permafrost also makes construction of new plants difficult. The common forms of phosphorus in wastewater are orthophosphate (PO4),
polyphosphate as polymers of phosphoric acid and organically bound phosphates.
Polyphosphate, such as hexametaphosphate, slowly hydrolyze in water to the
soluble ortho form. Biological uptake and chemical precipitation focus on the
removal of orthophosphate (from wastewater treatment) because orthophosphate is
the most abundant phosphorus species. Metal salts of aluminum or iron are
mostly used to precipitate phosphates chemically. Bacterial decomposition of
organic compounds also could release orthophosphates. Because the majority of phosphorus
compounds in wastewater are soluble, phosphorus is removed only in sparingly by
basic sedimentation process. Conventional wastewater treatment like
sedimentation and activated sludge alone removes only approximately 20 to 40
percent of the influent phosphorus.
Chemical and biological phosphorus removal process
Chemical
precipitation treatment by aluminum or iron coagulants is still used because it
is very effective to remove P. Most plants in the world use chemical phosphorus
removal strategy because it is a fast way to remove phosphorus at
a high level. Comparisons by other countries show that chemical phosphorus
removal produced more sludge than biological P removal and the difference is
dependent on the type of chemical used to remove P. Biological phosphorus
removal requires more energy because of the aeration used. Biological
phosphorus removal requires more energy in terms of the aeration capacity of
the process than chemical phosphorus removal and it also needs more space than
the chemical process as the anaerobic unit of the latter process could be skipped.
Sludge production combining chemical and biological P removal will save more
money. On the other hand using biological or chemical P removal individually is
not so efficient for saving money. But in some cases it is better to use one or
the other alone. For example with a lot of farm animal waste, chemical P
removal could save money and more efficiently remove P. It also depends on
which chemical is used or which biological treatment method is used. The point
of comparing biological and chemical P removal is to improve advantages and
minimize disadvantages. Write down which
methods can be applied in Mongolia and why so. Also write down which methods
are not suitable and describe the reasons.
Mongolian perspective
In
order to apply P treatment in Mongolia conditions, suitable methods (chemical,
biological or conventional) must be used to target the specific different types
of phosphorus forms and another elements present there which need to be removed.
Downstream of WWTP river polluted of high amount of nutrients and some other
elements (Mongolian national report,
2013). According to the WWTP data, most P-polluted water is from industry
which contains approximately 80% inorganic P. According to the research, conventional
treatment process removes only about 20 to 40 percent of influent phosphorus
compared to the biological method. The conventional method loses totally 70%
phosphorus (inorganic 3.05mg/l, organic 1.90mg/l) as the WWTP data shows P
organic and inorganic totally lose 7mg/l from this process. Combined chemical and
biological phosphorus removal loses approximately 18% of total phosphorus. In
18% of P loss includes inorganic 0.3mg/l, organic 1.0mg/l. This results, also
based on WWTP data, in P inorganic 4.0 mg/l and P organic 3.0mg/l. For control
and future perspective of capital city Ulan bator, wastewater treatment plant
according to my research need to apply combined method for get better quality
water. But we need to consider permafrost tolerant construction in order to
last long usage and plan for possible future increases in P in water.
Conclusion
In
conclusion chemical and biological phosphate removal process both are
acceptable in Mongolia, but only in constant condition, in other word it is
related to the climate and environment which it mean chemical and biological P
removal more efficient works in constant temperature and without . Furthermore, chemical P removal is better
than biological P removal in Mongolia because chemical removal process fast and
easy way to remove P from wastewater also takes small space of removal process
comparing to biological P removal. Biological removal required big space of
retain P.
Acknowledgement
My acknowledgement goes primarily to my supervisor Masud Parvage,
Doktorant student as a leading scholar in P removal in wastewater treatment
plant. He has provided support, motivation, insight and guidance. During the
process of research Masud motivated and checked my writing process. He has
provided me with correct guidance and valuable knowledge. He is young, talented
and kind hearted.
Reference
Biogeochemistry – element cycles data and
climate change spring 2014.
ADALBERT Oneke Tanyi Comparison of chemical
and biological Phosphorus removal in wastewater – A modelling approach.
JAMES L.BARNARD. 1976 A review of biological
phosphorus removal in the activated sludge process
HECTOR Garcı´a Martı´n., 2006 Metagenomic
analysis of two enhanced biological phosphorus removal (EBPR) sludge communitiesM.MAURER and M.BOLLER. 1999 Modelling of phosphorus
precipitation in wastewater treatment plants with enhanced biological
phosphorus removal
Nice blog
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