Novel helical or coiled flocculator for turbidity reduction in drinking water treatment: a performance study
https://doi.org/10.31219/osf.io/9nmzs
Since 1970s all PDAM have applied conventional technology in
water treatment plant because science and technology have not found an
innovative design yet[1]. All PDAM do not have a new design
and Ministry of Public Works have tended to implement IPA Kedasih (Instalasi
Pengolahan Air Keluaran Direktorat Air Bersih). Whereas the quality of raw
water vary widely from one island to another. Water in Java island has much
suspended solid and different from Sumatera, Kalimantan, Sulawesi, Papua where their
water is rich with natural organic matter. Edzwald[2] has examined natural organic matter
(NOM) in such research and found that NOM was more influential than turbidity
in controlling the coagulant dose. Ashery, et.al[3] also found the best removal
efficiency on NOM with spiral clari-flocculator.
Since that decade PDAM have used
baffled flocculator both in rectangular and hexagonal. Baffled flocculator is
an alternative to mechanical flocculator. Unfortunately, baffled flocculator
has a lot of sediment at its compartment’s corners therefore reduce its performance.
However, baffled flocculator is still used today because the consultants who
designed flocculator in water treatment projects have not had much knowledge yet
about helical flocculator. Efforts have
been made to reduce sediment with helical flocculator, an innovation in drinking water treatment technology. Since 1980s there has
not been much more research yet published. Some literatures used different
terms: helical, helicoidal, helix, spiral, coiled. All terms have the same meaning and
interchangeable. The first performance study has been done by Arfandy[4] and furthermore by Harjoko et.al[5], Vigneswaran and Setiadi[6], Hameed, et.al[7]. In their research, flowrate,
turbidity, and dimension of flocculators were different to each others.
In the field of hydraulic study and
fluid dynamic in flocculation process, it was investigated by Sartori et.al[8]. Tambo and Hozumi[9], Tambo and Watanabe[10] have examined floc characteristics,
floc strength but they did not use helical flocculators. In other method, Carissimi and Rubio[11] have studied the influence of compressed air to
flocculation process. Oliveira and Teixeira[12] have researched the performance of helical
flocculator for turbidity removal. In Indonesia there
has not been research yet on this flocculator after Arfandy[4], Harjoko et.al[5] but perhaps in different type or different
nomenclatur like hydrocyclone[13]. There are some differences in
shape, configuration, and process mechanism compared to helical flocculator.
Optimum performance in turbidity removal efficiency, sediment
volume, velocity gradient and detention time are the objective of this research.
Experiments are carried out using two pipe sizes and two helix diameters.
Helical flocculator produces less sediment than baffled flocculator. The
circular shape in layers is the advantage of helical flocculator but it is also
the difficulty when making circular pipe in layers, especially at big flowrate. It is more difficult than rectangular shape
or hexagonal baffled flocculator if using large diameter of steel pipe. But it ease
to implement in laboratory with small flowrate and no difficulty in setting the
apparatus.
The helical flocculators studied by authors mentioned
above used different pipe sizes and different helix diameters. Sartori et.al[8] used
helical flocculator in horizontal but in this study the helical flocculator was
installed vertical. All researchers used laboratory scale with variation in
pipe sizes and helix diameters. Researchers used hose or pipe for helical flocculators.
Another objective of this study was on small flowrate compared to previous studies
by researchers mentioned. It is hoped that small flowrate is more applicable to
small community of the city. If a larger flowrate is needed, then more than one
helical unit can be built and installed parallel. It is an alternative solution
for larger community. This study also run on medium turbidity concentration
i.e. 150 NTU. If the performance of small flowrate is good enough, the results
of this research can be widely known and become more popular among consultants
and governments.
Therefore it may enrich academic or scientific information
on efficiency (performance), velocity gradient (G), and detention time. The most important thing in design of hydraulic
flocculator is G value and can be maintained in one compartment therefore it
could not breakdown the floc. This is the reason why this hydraulic type is more
suitable to be applied in small and relative constant flowrate. With regard to
detention time (td), the flocculator requires more time than the coagulator
unit for its floc growth. The usual values written on textbooks are 20–60
minutes or 25–55 minutes[14][15][16].
In addition to pipe diameter, another parameter which
also plays an
important role is the helical
diameter. According to its function,
the helical diameter can be
adjusted to obtain a large G value at the inlet of helical flocculator and
then decrease gradually to the outlet. The
position and shape of helical
flocculator can be arranged with any unit in water treatment plant. If
the water treatment plant
(IPAM: Instalasi
Pengolahan Air Minum) is equipped with diffused aerator so the helical flocculator can be
installed in circles outside the aerator body. The installation can be
horizontal or incline depends on the desired
hydraulic effect and artistic consideration[17].
