< Previous48 MASTER BUILDERS JOURNAL #118 Community & Social Events CS 17 JANUARY 2020 MBAM Fellowship 1/2020 18 JANUARY 2020 MBAM Council Members Spread Joy to Children of Rumah Charis Foo handed red packets while other Council Members distributed gift bags to the children. Wishes of “Gong Xi Fa Cai” echoed in the air as they received their red packets from council members were used to buy essential household items for the Home’s usage. MBAM hopes this small gesture bring cheers and provide, in a small way, the needs As part of MBAM’s efforts to give back to the community, some 20 Council Members and secretariat staff, led by President Foo Chek Lee, visited Rumah Charis – Home for the Children (the Home) at Taman Yarl, Kuala Lumpur. Andrew Lim, who spoke on behalf of the Home, shared on the history of the home and its initiatives to provide shelter, education for the children as well as to nurture their inner talents. He thanked MBAM for spreading lunar joy to the children and hope more organisations will come forward to lend their support to the Home. A session to get to know the children was held before President Council members and secretariat with the children Jotun Paints (Malaysia) Sdn Bhd started the ball rolling, sponsoring the first fellowship for year 2020 that attracted some 95 participants. MBAM Fellowship 1/2020 was held at Muito Bom Brazilian BBQ Restaurant at Nexus, Bangsar South, Kuala Lumpur. In his speech, Managing Director of Jotun Paints (Malaysia) Sdn Bhd, Claudio Iurrili thanked MBAM members for supporting the event and for being given the opportunity to host the first MBAM fellowship of Secretary-General 1 and Chairman of MBAM Fellowship Committee, Ong Ka Thiam thanked Jotun Paints (Malaysia) Sdn Bhd for graciously sponsoring the event. As a token of appreciation and to commemorate the event, MBAM Deputy President, Tan Sri Haji Sufri Mohd Zin presented a souvenir to Iurrili. MBAM hopes more members will seize the opportunity to attend or sponsor MBAM fellowships as it is one of the best ways to build or develop Group photoCouncil members with Iurrili and Jotun staff Tan Sri Sufri (centre) presenting a souvenir to Iurrili accompanied by Ong (left)49 MASTER BUILDERS JOURNAL #118 Community & Social Events CS 12 FEBRUARY 2020 Latest update on 2019 Novel Coronavirus (COVID-19) in Malaysia: Giving Clarity by Datuk Dr Noor Hisham Abdullah – Director General of Ministry of Health Malaysia entrance. Those with a temperature of 37.5˚C and above should be isolated and asked to seek immediate medical attention. Organisers are advised to provide hand santinisers at the entrance and exit of the events and to have medical personnel on standby. Another attendee expressed his concern on the safety measures taken by the Government at hospitals. Datuk Dr Noor Hisham gave his assurance that all hospitals in Malaysia are well equipped with the latest technologies, knowledge, and updates. He mentioned that nurses and doctors are the front liners who deal with patients and have higher risks of exposure to the virus. However, with proper training and precautionary measures being observed at all hospitals, Datuk Dr Noor Hisham assured that the situation is well under control. He quoted the cases of the first Malaysian guy being tested positive after he caught the flu and fever upon returning from a conference in Singapore and the Malaysians and their family members who were brought home from Wuhan via the Humanitarian Aid Mission. They were all checked thoroughly and treated professionally. As of the date of the event, there were 22 confirmed cases in Malaysia with no fatality reported and 9 confirmed cases has been discharged from hospital. Before the event ended, Datuk Dr Noor Hisham pleaded and reiterated to the attendees not to spread rumours in the social media as it might cause a panic. He added that the ‘virus’ spread in social media is creating the same impact as the COVID-19. The Government (the Ministry of Health) will update the public regarding COVID-19. The event organised by Informa Markets was held at Malaysia International Trade and Exhibition Centre (MITEC), Kuala Lumpur. MBAM Vice President, Dennis Tan and Council Member, Datuk Astaman Abdul Aziz were present to receive the latest information and advice from the Ministry. The organiser, Informa Markets Group Managing Director, M Gandhi apologised for the last-minute invitation notice during the opening speech before Chairman of Malaysia- Informa Markets, Tan Sri Asmat Kamaludin delivered his welcome speech. The highlight of the event was the presentation of scientific facts and data by Director-General of Health Malaysia, Ministry of Health, Datuk Dr Noor Hisham Abdullah. During his speech, he gave assurance to all members of the public that the situation is well monitored and pleaded to everyone to not disseminate fake news about the COVID-19 in the social media. He added that COVID-19 is a new virus strain and that it was still unclear how it spread so fast. He advised everyone to take care of their personal hygiene at all times. Datuk Dr Noor Hisham advised those who are at risk or suspected of contracting the virus to fill in the self- declaration form, especially those returning from affected countries like China, Japan, and Singapore, and to seek medical advice immediately. Those who are unwell with symptoms such as running nose, fever, severe cough and difficulty in breathing are advised to isolate themselves from loved ones, the community, and the public. Infant, small children, pregnant women, and old people are more prone to infection compared to adults, due to their weaker immune systems. During the Q&A session, one of the attendees addressed the impact of organising events during this period. Datuk Dr Noor Hisham responded that it is the responsibility of organisers to defer. If they decide to proceed with the events, he advised that every single person attending the event must get their body temperature checked at the IMAGE: CENTERS FOR DISEASE CONTROL AND PREVENTION 50 MASTER BUILDERS JOURNAL #118 Community & Social Events CS InBrief celebration was held at Shen Jai High School, Ipoh, Perak. Perak Plumber’s Association 45 th Anniversary 13 DECEMBER 2019 held its 28th Anniversary Dinner at Ideal Convention Centre, Selayang. Malaysia Heavy Construction Equipment Owners’ Association 11 JANUARY 2020 was hosted by President, Foo Chek Lee for Council Members and Secretariat staff at Unique Seafood, Petaling Jaya. MBAM Chinese New Year Dinner 31 JANUARY 2020 celebrated its 48 th anniversary at Restoran Kaw Loon, Kampong Baru, Alor Setar. Kedah Contractors & Building Material Supplies Association 15 JANUARY 2020 Lighthouse Club KL December 2019 Get Together was held at Havana, Changkat Bukit Bintang, Kuala Lumpur. 5 DECEMBER 2019 Huazong 2020 Geng-Zi (Metal Rat) Year Chinese New Year Celebration was held at Wisma Huazong. 3 FEBRUARY 202051 MASTER BUILDERS JOURNAL #118 Community & Social Events CS InBrief was held at PAM Centre. Kuala Lumpur Architecture Festival 2020 Launch & PAM Chinese New Year Open House 2020 15 FEBRUARY 2020 was held at El-Sids Pub, Kuala Lumpur. Lighthouse Club Kuala Lumpur Chinese New Year Get-together 6 FEBRUARY 2020 was held at its premises. Selangor and Wilayah Kin Cho Hong Chinese New Year Celebration 7 FEBRUARY 2020 held its Chinese New Year celebration at Copper Mansion, Petaling Jaya. Building Materials Distributors Association of Malaysia 13 FEBRUARY 2020 held its Chinese New Year celebration at Wisma IEM. The Institution of Engineers Malaysia 7 FEBRUARY 2020 National Council for Occupational Safety and Health’s (NCOSH) Occupational Safety & Health Excellence Awards 28 FEBRUARY 2020 was held at the Palace of the Golden Horses, Selangor.52 MASTER BUILDERS JOURNAL #118 Feature BY IR NEOH CHENG AIK Slope Stability Problems Part 2 Part 2 on the overview of slope stability problems, aimed at providing insights on how a slope can be stabilised or destabilised by various factors. The common stabilisation and protection methods for slopes with particular reference to applications, limitations and their engineering basis will also be briefly discussed. Statistics about Slope Failures e) Other statistics about Landslides Ashaari & Hassandi (2009) has reported that there were about 500 reported landslides and about 500 people killed by landslides in Malaysia since 1961 (about 10 people/year killed) with a total estimated economic loss of RM 2.5 billion from 1973 to 2007 (about RM 73.5 million/year). Recent high profile landslides involving with fatalities are Highland Tower Landslide (48 killed,1993), Genting Slip Road Debris Flow (20 killed, 1995), Gua Tempurong Landslide along North-south Expressway near Tapah (1 killed, 1996), Pos Nipang Perak Debris Flow (44 killed, 1996), Keningau Sabah (302 killed, 1996), Taman Hillview landslide (8 killed, 2002), Bukit Antarabangsa landslide (5 killed, Dec 2008), Penang Tanjung Bungah landslide (11 killed, 2017), etc. All these massive landslides have common characteristics of very large upslope catchments, which provide large surfaces to excessive infiltration, which is cited for 90% of slope failures. Most of these landslides also have adverse geological discontinuities causing deep saturation. f) Summary of statistics The above statistics reinforce the importance of provision of adequate and effective slope protection and drainage for surface runoff and subsoil. Infiltration due to surface runoff from large upslope catchments, extensive relict FIGURE 2 Main Common Causes for Slope Failures Fig 4 is modified from Mohd Haris Abas (1983) • Reliable SI refers to SI by CIDB registered SI Contractor using proper equiment, proper test procedure & under supervision by qualified personnel. Adequate SI refers to scope of SI that meet the requiments by established guidelines such as REAM GL6/2004, etc. BEM CIrcular 4/2005 reminds all Professional Engineers of thier responsibility of SI works. • Refer JKR “Guidelines for Slope Design” (Jan 2010) FIGURE 4 Interrelated Causes & Effects for Slope Failures Inadequate/bold design due to inexperience/ carelessness/ignorance of designer/checker Inadequate or unreliable S.I. or poor S.I. interpretation Inadequate geological assessment (no geological mapping for geological discontinuities for cut slopes) Miscellaneous such as high water or seepage pipe leakage, etc. 2 3 5 4 1 Unawareness Inexperience Ignorance Carelessness False economy Greed Attitude Inadequacy in S. I. design & assessments Defective construction Poor workmanship Lack of quality supervision Lack of proper method statement Lack of reported case histories (Ref.) Misuse of slope Excessive infiltration Saturation & loss of matric suction Toe inundation, collapse settlement Erosion Creeping/cracks/peak to residual shear strength Ultimate slips Human FactorsTechnical ShortfallsSlope Distress/Failure Infiltration due to excessive surface runoff as the result of inadequate drainage, poor slope protection, extensive relict geological discontinuities, large upslope catchments, etc. Slope Failure CausesEffects53 MASTER BUILDERS JOURNAL #118 Feature geological discontinuities or poorly drained and protected slopes can result in an extensive increase of saturation and a subsequent loss of suction and shear strength simultaneously. Effective measures against infiltration are therefore effective methods to avoid landslides. Main common causes for slope failures and interrelated causes and effects of slope failures are summarised and illustrated in Figures 2 and 4 respectively. Slope Design Methods There are many methods and procedures or approaches to assess stability and design of slope stabilisation works, but generally and usually, the methods can be broadly classified as analytical method and precedent method. State-of-the art for slope stability analysis remarked by Brand (1985) are as follows: • Modeling & mechanism: very good – good • Shear stress (soil density, H, WT, etc.): very good – good • Shear strength (c’, Ø’): fair – good • Shear strength (suction/pore pressure): poor – very poor Peak shear strength can be high when unsaturated or dry, but can be reduced to residual strength when the slope suffers creeping (high strain) after excessive infiltration and saturation, especially when cut slope is steep and there are extensive relict geological discontinuities or large upslope catchments. Fill slope with excessive subsoil seepage or toe inundation or excessive infiltration can also cause extensive saturation, collapse settlement and creeping, especially when compaction is inadequate and the fill has collapsible minerals. a) Analytical method refers to a rigorous and time-consuming method based on detail site survey, site investigation and laboratory tests. This rigorous method is normally justified for high risk to life and high economic risk structures, such as high slopes near high-rise buildings, deep excavation near buildings, or important structures. Detailed design validation, including geological mapping and monitoring of slope performance are also parts of the analytical method. This method shall only be carried out by experienced geotechnical engineers and independently checked by BEM accredited checkers or experts. The most challenging/difficult part (time- consuming and costly/expensive) for the success of this method is to get adequate quality undisturbed samples at distinct strata for CIU tests and determination of realistic groundwater conditions, especially the perched water table. b) Precedent method is generally based on precedent experience and some limited SI and surveys during the design stage, but detail assessments and design review are carried out during the construction stage, after more specific and detailed information are available. This method is simple and faster but is more applicable and practical for urgent projects involving many slopes, such as highway projects. This precedent method should have scope of design validation, including geological mapping, block samples for CIU tests at distinct layers for stability analysis review, etc., especially for cut slope height exceeding 12m. This method is summarised in Figure 3. Fill slope design scope is given in Figure 1. FIGURE 3 Cut Slope Design (Precendent Method) a) Based on statistical survey of cut slopes along KL-Karak Highway, generally 1:1 cut slopes with minimum 1.5m to 2.0m berms cut of max 6m vertical intervals shall be statistically stable (FOS>1.2) provided the following assessments & design validations are carried out by qualified geotechnical engineers. • Adequate & effective cast-insitu surface drains & slope protection works (refer Fig 5) shall be provided • Provide horizontal drains at strata underlain by comparatively impermeable strata or if seepage is observed at site. • If adverse relict geo discontinuities are present, provide impermeable slope protection such as guniting or HDPE geocell with underlying membrane plus horizontal drains, etc. • In case large upslope catchment is encountered, it should be engineered by qualified engineers to ensure compliance with the basic requirements recommended by “Geotechnical Manual for Slopes” (GEO Hong Kong, 1984). Mitigations to reduce infiltration such as more interceptor drains, horizontal drains, provision of impermeable surface, etc., should be provided. • Earthwork practice shall comply with the requirements of Nota Teknik (J) 20/98. b) Adequate scope of SI for cut slope design as per REAM GL6/2004 shall be carried out to assess slope stability (prelim design). Water table shall be monitored by piezometers especially at potential perched water table. c) In case of inadequate FOS, proper methods of slope stabilization as discussed in Para. 7 shall be considered. d) Unless design review by BEM accredited checker & adequate design validation during construction stage are carried out by suitably qualified P Eng, this precedent method is not recommended for • Cut slopes exceeding 18m high and/or slopes with high risk to life or high economic risk structures • Cut slopes with large upslope catchments and slopes with extensive relict geological discontinuities. e) Shear strength for stability analysis shall be validated by insitu shear box tests for gravelly soils or block/Mazier samples taken at representative distinct strata and at relict discontinuities (if any) for CIU tests during the construction stage. f) Flexible Debris Flow Barriers shall be constructed for large and long connected valleys at upslope catchments to reduce the risk of debris flow (Asbi, et, al, 2008).54 MASTER BUILDERS JOURNAL #118 Feature This method is very popular among designers because it is practical and fast. Success for this method requires a lot of comparable local experiences and reported case histories to justify the design. Stability analysis can be based on deduced or correlated shear strength parameters from some SI or reported typical values (Refer to Table 8 of Geoguide 1, GEO Hong Kong). The precedent method can be as reliable as that of an analytical method if the design verification scheme and mitigations as stated in Figure 3 are truly carried out. The main difficulty and problem of this method is to identify the WT, seepage, upslope catchment conditions and the unstable geological discontinuities/ settings during the construction stage, and provide due effective mitigative measures against infiltration. The success of this method requires the committed site engineer to ensure the necessary design validation and review are truly and duly carried out during the construction stage. This method is soundly based on statistical study/ comparable experiences and provision of adequate and effective mitigations against infiltration, which is cited as a major cause for slope failures. JKR’s ‘Guidelines for Slope Design’ (Jan 2010) provides some useful design guidelines for rock, cut and fill slopes with particular reference to slope design requirements for site investigation, geological mapping, independent check for slope stabilisation, design criteria plus typical details of soil slope stabilisation methods, etc. Slope Protection Methods Proper slope protection can not only prevent slope surface erosion due to surface runoff, etc., but can also reduce infiltration, which is the main culprit for slope failures. Proper slope protection can also enhance slope FIGURE 3B This cut slope at the road level has very large upslope catchments that are prone to excessive infiltration. Adequate mitigations against signs of excessive infiltration plus instru- mentation should be provided to mitigate against landslide. FIGURE 3A This cut slope has no large upslope catchments for excessive infiltration. No sign of seepage, no severe geological discontinuities except some localised boulders. Hence, with proper slope protection and slope drainage, the risk of excessive infiltration is practically negligible or the slope is bound to be safe and stable. Some block samples from distinct layers should be taken for CIU tests for quantitative stability analysis to ascertain the local and global stability. With regular routine inspection and maintenance by suitably qualified personnel as per recommendations by JKR Guidelines on Slope Maintenance in Malaysia (Aug 2006) and some simple instrumentation monitoring, the slope should be reliably able to ensure long safety and stability. FIGURE 1 Design of Fill Slope/Embankment Scope of design to ensure compliance with design criteria (Refer JKR Nota Teknik (J) 20/98): 1. Foundation Stability: Check FOSb vs. bearing failure & post construction settlement. 2. Slope Stability Analysis: Check FOSs vs. slope slip. If FOSb <2 (long term) &/or FOSs< 1.2, design the necessary ground treatment & slope stabilisation. 3. Toe Stability Design: Design/provide toe stabilisation (rock toe/reinforced toe) for the toe likely to be inundated or high capillary action, etc., or high fill slopes (>18m). 4. Slope Protection Design: Check slope geometry & soil type & select suitable slope protection method (refer Fig 5). 5. Slope Drainage Design: Refer REAM Guidelines for slope drainage design.55 MASTER BUILDERS JOURNAL #118 Feature appearance to ensure an aesthetically pleasing environment. It has been reported that bare or poorly vegetated slopes have three to five times more infiltration rate than the properly vegetated slopes. Factors that can affect selection of suitable slope protection methods are given in Figure 5 and Figure 6. Various types of slope protection and the applications/limitations are briefly discussed. To be continued in Part 3 Ir Neoh Cheng Aik is a Director of E-Geo Consultants Sdn Bhd and frequently engaged as a geotechnical design checker and expert witness in construction disputes. He was the past Vice President of IEM, past Chairman of Geotechnical Division of IEM and past Chairman of REAM Technical Committee (TC 5) Geotechnics. FIGURE 5 Slope Protection Selection Chart 1. SOIL TYPE 1.1 Silty/Sandy CLAY 1.2 Sandy SILT 1.3 Silty SAND 1.4 Fractured/Rocky Boulderly 1.5 Very stiff/hard 1.6 Acidic 2 SLOPE GEOMETRY 2.1 Gentle slope, B < 350 2.2 Medium slope 2.3 Steep slope, B > 42 0 2.4 Down-slope length, L > 10m 3 MISCELLANEOUS 3.1 Aesthetic 3.2 “Green” requirement 3.3 High water table 3.4 Poor slope surface drainage 3.5 Shady area 3.6 Unit cost (RM/m2) x ? ? ? x ? ? < 8 ? x x ? x ? ? ? < 3 ? ? x ? ? < 5 ? x ? ? ? ? x < 5 ? < 50 ? ? x ? x < 70 x ? < 70 x x < 90 x x < 100 Close Turfing Hydro- Seeding Hydro- Seeding with Biomat Vetiver Grass HDPE Geocell Gabion Mat- tress Stone Pitch- ing RC Skin WallGuniteConditions Methods* Legend: very suitable suitable ? doubtful x not suitable Close Turfing Gabion Mattress Stone Pitching Vetiver Grass Guniting R.C. Skin Wall HydroseedingHDPE Geocell56 MASTER BUILDERS JOURNAL #118 Feature BY ROMEO ROGER & BEN LOW B.T. Application of Membrane Bio-Reactors (MBRs) in Wastewater Treatment Plants The use of Membrane Bio-Reactors (MBRs) is common in industrial wastewater treatment plants but not in domestic sewage treatment plants. However, as the technology matured and membrane cost reduces, the benefits of using MBRs are now steadily outweighing the once-considered high capital investment. M embrane Bio-Reactor (MBR) usage in wastewater treatment plants have been around since the 1960s. The adoption of the technology is prominent in many western countries such as Germany, Greece, Spain, England, Italy, USA, Mexico, as well as Asian countries such as China, South Korea, Japan, and many others; including our neighbour, Thailand. It is, however, not the norm in Malaysia until today. Membrane Bio-Reactor still employs the concept of a suspended growth activated sludge at its core. Biological treatment also still happens in an aeration tank. However, unlike the conventional activated sludge plant, membranes are utilised for the solid-liquid separation process instead of a secondary clarifier. CONVENTIONAL SYSTEM FOOTPRINT: 100MBR TREATMENT FOOTPRINT: 25-30 FIGURE 1 Comparison Between a Conventional Plant and an MBR Plant57 MASTER BUILDERS JOURNAL #118 Feature Another noticeable difference with conventional plants is that MBR plants operate with much higher MLSS in the biological reactor, typically at a level of 10,000 mg/L compared to around 4,000 mg/L in a conventional plant. Although the difference seems to be minimal (the use of a membrane instead of a secondary clarifier), the effect on the plant is huge in terms of the advantage gained. For instance, the lack of a physical secondary clarifier reduces the footprint of the plant. The operation of an MBR plant with high MLSS also reduces the biological reactor footprint, as a higher MLSS reduces the need for a large biological reactor while maintaining a similar efficiency. High quality effluent is also achieved by using a membrane for solid separation. An ultrafiltration membrane especially, allows for bacteria and virus removal, eliminating the need for a separate disinfection process in the same plant. All of these combined provide the main advantage of a membrane bio- reactor, which has a small footprint compared to a conventional extended aeration plant. An MBR plant footprint can be as small as 25-30% compared to conventional plants, as illustrated in Figure 1. Revisiting the topic of the effluent quality of a membrane bio-reactor plant, Table 1 shows the typical effluent quality that can be achieved with this technology. The permeate quality of an MBR plant definitely surpasses a conventional plant and the industry standard of a wastewater treatment plant. The question then is what we can do with the treated effluent. It would be a waste to discharge high-quality treated water back into the river if it can be re-used for other purposes. Let’s take the example of the first MBR plants in Malaysia for domestic sewage, installed for The Exchange 106 tower at the heart of the TRX development in Kuala Lumpur. The treated effluent was re-used for the building’s usage. Instead of connecting the building sewage into the main sewage treatment plant, the developer decided to build their own treatment plant within the building. In order to achieve a zero-discharge plant, an MBR plant was implemented to produce high-quality effluent. The final treated effluent can then be used as make-up water for the cooling tower as well as toilet flushing and landscape irrigation. Imagine, The Exchange 106 are able to self-produce 1,000 m 3 /day of water from the treated MBR effluent. Based on an estimated potable water cost of RM 2.28/m 3 , The Exchange 106 is then able to save up to RM2,280.00 per day. Due to the compactness of the MBR plant, the developer only needs to allocate a mere 562 m 2 > of space to construct a sewage treatment plant with a 5,700 PE (1,300 m 3 /day) capacity, located at the basement of the building. Assuming that the land cost is RM3,000.00 per sqft., this STP uses up only an estimated amount of RM18.0 million of land cost. In contrast, if The Exchange 106 installed a conventional STP, such as the Extended Aeration (EA) and Sequential Batch Reactor (SBR), it would require 75% more space than the MBR plant. The extra space would cost an additional estimated amount of RM54.0 million. This project in particular, has been a step forward in enriching the national level of wastewater treatment expertise. The membrane technology also opened up more possibilities in how wastewater effluent can be re- used. In the current situation where water supply is becoming more and more precious, re-using the treated effluent in such a way instead of allowing it to be discharged, is now becoming a more attractive and affordable option. This has been made possible by adapting technologies such as the MBR in wastewater treatment plants. Although the technology has existed for quite some time, our nation has been quite slow on the uptake and in making use of such technology. Therefore, it is perhaps time we nudge the industry forward to be more open to beneficial technologies, such as MBR in domestic sewage treatment. Various industries, such as property development and manufacturing, will certainly find this technology beneficial in their operations. Reference list of abbreviations: MBR Membrane Bio-Reactor MLSS Mixed Liquor Suspended Solid BOD 5 5 Days Bio Chemical Oxygen Demand TSS Total Suspended Solid NH4-N Ammoniacal Nitrogen TP Total Phosphorous TN Total Nitrogen EA Extended Aeration SBR Sequential Batch Reactor Article courtesy of OCNED Water Technology Sdn Bhd. For further information, please contact enquiry@ocned.com / www.ocned.com TABLE 1 Typical Treated Water Quality of the MBR System The authors, Romeo Roger and Ben Low B.T. are the Senior Design Engineer/Head of NRW and Sales Engineer at OCNED Water Technology Sdn Bhd respectively. * With coagulation PARAMETERS BOD5 TSS NH4-N *TP TN Turbidity PERMEATE < 5.0 mg/L < 2.0 mg/L < 1.0 mg/L < 1.0 mg/L < 10 mg/L < 10 mg/L INFLUENT 250 mg/L 300 mg/L 30 mg/L 10 mg/L 50 mg/L -Next >