9 months ago


Water treatment

The length of this

The length of this ripening period is similar to that reported at the beginning of section 3.2.4 for pilot SSF units at Puerto Mallarino and lower than those reported by Haarhoff and Cleasby (1991) from SSF units operating in the seasonal environment of the USA. As pointed out in Section 3.2.4, it seems that the ripening period for turbidity could be used as an indicator of ripening for bacteria, including a time safety factor, but only in those small WS systems with limitations for microbiological analyses. However, This possibility requires further observations before making any practical recommendation. Besides, low turbidity levels (< 5 NTU) will also improve the effectiveness of terminal disinfection. The technological concept of “ ripening period” and its implications for the O&M of MSF plants, must be shared with caretakers and community leaders to reduce the risk of affecting public health by connecting recently scraped units before they mature. This is particularly relevant in systems with two SSF units due to the small flow buffering capacity available at the treatment plant and possible complaints of users. 10000 Faecal Coliforms (CFU/100 ml) 1000 100 10 1 0 10 20 30 40 50 Running time (days) 60 25 50 20 Colour (PCU) 40 30 20 15 10 Turbidity (NTU) 10 5 0 0 0 10 20 30 40 50 Running Time (days) Colour(PCU) Turbidity (NTU) Figure 4.17 Faecal coliform, turbidity and colour level in effluents of SSF 1 of Retiro treatment plant after resanding activities. August, 1999. 167 Operation and Maintenance aspects of MSF plants Local operators, with low level of schooling (< 5 years), having the support of local administrators or community based organisations, were operating all MSF plants. Before and during the operation of the plants they participated in workshops including O&M activities organised by Cinara, in collaboration with water related institutions active in the Cauca Valley Department. After an initial unstable period, the local administrative and operational staff have become more stable, as shown in table 4.1. However, this is not the case with technical and professional staff from water related institutions, which are still showing frequent changes in spite of the decentralisation process in the water sector in Colombia. Although there was not systematic monitoring of O&M activities, some practical observations are summarised below to illustrate this dimension of the present experience • PCA (Partial cleaning activities: bottom drainage and surface raking) of DyGF units were accomplished once or twice a week on average. Surface raking is illustrated in photo 4.20. TCA (total-cleaning activities, including gravel bed excavation) were executed every 3 to 6 months. • PCA of CGF units (Upflow and horizontal flow coarse gravel filters) have been adopted in different ways at local level. Short hydraulic cleaning, (bottom drainage only. Illustrated in photo 4.22 and 4.23) varied from daily to once or twice a week. Hydraulic and manual cleaning (bottom drainage complemented with surface shovelling in the case of upflow units) varied from once a week to once a month. TCA of CGF units (including gravel bed excavation) were performed in Retiro during the construction of 2 nd phase. Based on available information, practically all CGF units have been operating without undergoing TCA, meaning 4 to 12 years of continuous operations. • Mean SSF run lengths are shown in figure 4.16. PCA activities (scraping, photo 4.21) are completed in less than a working day in all MSF plants. TCA (Resanding) are taking place every 4 to 6 years approx. However, due to the high cost of land in the south-west part of Cali, some local institutions and community based organisations decided not to build sand storage facilities (e.g. Retiro). Therefore, the sand is replaced every time the SSF units are scraped. As Huisman and Wood (1974) found, deposits accumulates from run to run in sand beds making it necessary to excavate around 0.2 to 0.4 m of sand depth during otherwise normal scraping procedures. This practice increases running costs of the systems and would reduce their sustainability in communities without capacity to pay for additional labour during these more demanding scraping procedures. Observations concerning devices and hydraulic control facilities in MSF plants During the process of adapting or developing MSF technology to the Andean context, the author and colleagues introduced devices and hydraulic facilities to improve the impact and sustainability of the treatment projects. Some of them are summarised below. • DyGF stage was mainly developed to reduce the impact of SS in subsequent filtration stages, which are more costly and relevant to reduce acute risks. After overcoming initial design and construction limitations, it is performing well in most treatment plants. However, removal efficiencies at DyGF stage in Cañasgordas are low (table 4.8) due to the high filtration rate (8.7 mh -1 ) and short gravel bed depth (0.3 m) specified in its design (table 4.2). Removal efficiencies are also low at DyGF stage in Javeriana due to its short gravel bed (0.3 m). Based on the results of the present research work (Section 3.2.3), lower velocities (< 4 mh -1 ) are now recommended. • Frequent hydraulic cleaning activities of coarse gravel filters require fast opening valves to drain the units, including the option to introduce changes in the flow pattern inside the gravel beds. Annex 1 includes examples of two early designs for these types of valves, based on experiences 168

Screen Filtration for Ballast Water Treatment Applications - Cross ...
Pall Aria™ AP-Series Packaged Water Treatment ... - Pall Corporation
Precursor Removal from Ground Water Using GAC ... -
Water Treatment Improvements and Plant Capacity ... -
Pall Aria™ AP-Series Packaged Water Treatment ... - Pall Corporation
The best solutions in water treatment - Istobal
The Treatment of Scottish Water for Private Communities
2003 City of Roanoke Water Quality Report - Western Virginia Water ...
Council Bluffs Water Works South Water Treatment Plant – Planning ...
Water Treatment Products - Colorfil
Pilot Testing and Evaluation of Three Filtration Technologies - pncwa
Microorganisms (The Coliform Group Bacteria)
Capacity Charts for Water Treatment Systems
Technical Advances in the Treatment of Water and Air for ... - IAAPA
FILTRATION - Environmental Protection Agency
Filter housings catalogue
Chemicalfree Water Treatment - Necon
Weatherford in Waste Water Treatment (WWT)
Commercial water treatment solutions - CMS
Evaluation of Treatment Options for the Raspberry ... - Loudoun Water
environmentally responsible water treatment - Promolife
Information You Need to Know When Considering ... -
Drinking Water Treatment for Small Communities - P2 InfoHouse
Water Quality Report - 2010 - Presidio Trust
Omnipure catalogue - The Water Shop