Novel Helical or Coiled Flocculator

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].