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舊 2017-11-23, 23:40     #1
mizyeh 的頭像
居住地 : 汐止
魚缸尺寸 : 2呎立方
系統類別 : FO
生物類別 : 黃三角、藍倒吊、皇后
發文總數 : 292
註冊 : 2012-12-12
造訪 : 2019-01-12 12:51
探索 KH 對 FO 重要的可能原因


閒逛本站贊助商魚單時,看見小張《水質處理KH值》老手不說 新手不懂的關鍵水質因子 這篇文章,
拿出塵封已久的試劑量了下KH,果然得到 3.x dKH這樣的數據。

這幾天每當想起此事便上網搜尋,關鍵字從「KH FO」開始,隨著拜讀文章內容的轉變,一路到 「nitrate alkalinity」,
最終找到這篇出自加州水資源協會網站的文章 How Alkalinity Affects Nitrification,主要是探討KH在硝化作用中扮演的角色,






#硝化作用在pH 7.0的效率,僅有pH8.0的一半不到。

Use alkalinity profiling in wastewater operations to control biological activity and optimize process control

By Mary Evans and Gary Sober

The Water Environment Federation’s new Operations Challenge laboratory event will determine alkalinity needs to facilitate nitrification. Operators will evaluate alkalinity and ammonia by analyzing a series of samples similar to those observed in water resource recovery facilities.

This event will give operators an understanding of how alkalinity works in the wastewater treatment process to facilitate nitrification, as well as the analytical expertise to perform the tests onsite. This provides the real-time data needed to perform calculations, since these analyses typically are performed in a laboratory that can present a delay in the data.

What is alkalinity?

The alkalinity of water is a measure of its capacity to neutralize acids. It also refers to the buffering capacity, or the capacity to resist a change in pH. For wastewater operations, alkalinity is measured and reported in terms of equivalent calcium carbonate (CaCO3). Alkalinity is commonly measured to a certain pH. For wastewater, the measurement is total alkalinity, which is measured to a pH of 4.5 SU. Even though pH and alkalinity are related, there are distinct differences between these two parameters and how they can affect your facility operations.

Alkalinity and pH

Alkalinity is often used as an indicator of biological activity. In wastewater operations, there are three forms of oxygen available to bacteria: dissolved oxygen (O2), nitrate ions (NO3– ), and sulfate ions (SO42-). Aerobic metabolisms use dissolved oxygen to convert food to energy. Certain classes of aerobic bacteria, called nitrifiers, use ammonia (NH3) for food instead of carbon-based organic compounds. This type of aerobic metabolism, which uses dissolved oxygen to convert ammonia to nitrate, is referred to as “nitrification.” Nitrifiers are the dominant bacteria when organic food supplies have been consumed.

Further processes include denitrification, or anoxic metabolism, which occurs when bacteria utilize nitrate as the source of oxygen and the bacteria use nitrate as the oxygen source. In an anoxic environment, the nitrate ion is converted to nitrogen gas while the bacteria converts the food to energy. Finally, anaerobic conditions will occur when dissolved oxygen and nitrate are no longer present and the bacteria will obtain oxygen from sulfate. The sulfate is converted to hydrogen sulfide and other sulfur-related compounds.

Alkalinity is lost in an activated sludge process during nitrification. During nitrification, 7.14 mg of alkalinity as CaCO3 is destroyed for every milligram of ammonium ions oxidized. Lack of carbonate alkalinity will stop nitrification. In addition, nitrification is pH-sensitive and rates of nitrification will decline significantly at pH values below 6.8. Therefore, it is important to maintain an adequate alkalinity in the aeration tank to provide pH stability and also to provide inorganic carbon for nitrifiers. At pH values near 5.8 to 6.0, the rates may be 10% to 20% of the rate at pH 7.0. A pH of 7.0 to 7.2 is normally used to maintain reasonable nitrification rates, and for locations with low-alkalinity waters, alkalinity is added at the water resource recovery facility to maintain acceptable pH values. The amount of alkalinity added depends on the initial alkalinity concentration and amount of NH4-N to be oxidized. After complete nitrification, a residual alkalinity of 70 to 80 mg/L as CaCO3 in the aeration tank is desirable. If this alkalinity is not present, then alkalinity should be added to the aeration tank.

Figure 1. pH versus nitrification rates at 68ºF (maximum nitrification rate occurs at 8.0–8.5 pH) Source: EPA-625/4-73-004a, Revised Nitrification and Denitrification Facilities Wastewater Treatment, U.S. Environmental Protection Agency Technology Transfer Seminar.

Figure 2. Measurement of nitrification activity at a pH of 7.2 and lower Source: EPA-625/4-73-004a Revised Nitrification and Denitrification Facilities Wastewater Treatment, U.S. Environmental Protection Agency Technology Transfer Seminar.

Why is alkalinity or buffering important?

Aerobic wastewater operations are net-acid producing. Processes influencing acid formation include, but are not limited to

biological nitrification in aeration tanks, trickling filters and rotating biological contactors;
the acid formation stage in anaerobic digestion;
biological nitrification in aerobic digesters;
gas chlorination for effluent disinfection; and
chemical addition of aluminum or iron salts.
In wastewater treatment, it is critical to maintain pH in a range that is favorable for biological activity. These optimum conditions include a near-neutral pH value between 7.0 and 7.4. Effective and efficient operation of a biological process depends on steady-state conditions. The best operations require conditions without sudden changes in any of the operating variables. If kept in a steady state, good flocculating types of microorganisms will be more numerous. Alkalinity is the key to steady-state operations. The more stable the environment for the microorganisms, the more effectively they will be able to work. In other words, a sufficient amount of alkalinity can provide for improved performance and expanded treatment capacity.

How much alkalinity is needed?

To nitrify, alkalinity levels should be at least eight times the concentration of ammonia in wastewater. This value may be higher for untreated wastewater with higher-than-usual influent ammonia concentrations. The theoretical reaction shows that approximately 7.14 mg of alkalinity (as CaCO3) is consumed for every milligram of ammonia oxidized. A rule of thumb is an 8-to-1 ratio of alkalinity to ammonia. Inadequate alkalinity could result in incomplete nitrification and depressed pH values in the facility. Plants with the ability to denitrify can add back valuable alkalinity to the process, and those values should be taken into consideration when doing mass balancing. (For Operations Challenge event, the decision has been made to not incorporate the denitrification step in process profiling.) To determine alkalinity requirements for plant operations, it is critical to know the following parameters:

influent ammonia, in mg/L,
influent total alkalinity, in mg/L, and
effluent total alkalinity, in mg/L.
For every mg/L of converted ammonia, alkalinity decreases by 7.14 mg/L. Therefore, to calculate theoretical ammonia removal, multiply the influent (raw) ammonia by 7.14 to determine the minimum amount of alkalinity needed for ammonia removal through nitrification.

For example:

Influent ammonia = 36 mg/L

36 mg/L ammonia ´ 7.14 mg/L alkalinity to nitrify = 257 mg/L alkalinity requirements

257 mg/L is the minimum amount of alkalinity needed to nitrify 36 mg/L of influent ammonia.

Once you have calculated the minimum amount of alkalinity needed to nitrify ammonia in wastewater, compare this value against your measured available influent alkalinity to determine if enough is present for complete ammonia removal, and how much (if any) additional alkalinity is needed to complete nitrification.

For example:

Influent ammonia alkalinity needs for nitrification = 257 mg/L

Actual measured influent alkalinity = 124 mg/L

257 – 124 = 133 mg/L deficiency

In this example, alkalinity is insufficient to completely nitrify influent ammonia, and supplementation through denitrification or chemical addition is required. Remember that this is a minimum — you still need some for acid buffering in downstream processes, such as disinfection.

Bioavailable alkalinity

Most experts recommend an alkalinity residual (effluent residual) of 75 to 150 mg/L. As previously identified, total alkalinity is measured to a pH endpoint of 4.5. For typical wastewater treatment applications, operational pH never dips that low. When measuring total alkalinity, the endpoint reflects how much alkalinity would be available at a pH of 4.5. At higher pH values of 7.0 to 7.4 SU, where wastewater operations are typically conducted, not all alkalinity measured to a pH of 4.5 is available for use. This is a critical distinction for the bioavailability of alkalinity. Therefore, in addition to the alkalinity required for nitrification, additional alkalinity must be available to maintain the 7.0 to 7.4 pH. Typically, the amount of residual alkalinity required to maintain pH near neutral is between 70 and 80 mg/L as CaCO3.

Proper alkalinity levels for treatment

Alkalinity is a major chemical requirement for nitrification and can be a useful and beneficial tool for use in process control. Several things to keep in mind:

Alkalinity provides an optimal environment for microscopic organisms whose primary function is to reduce waste.
In activated sludge, the desirable microorganisms are those that have the capability, under the right conditions, to clump and form a gelatinous floc that is heavy enough to settle. The formed floc or sludge can be then be characterized as having a sludge volume index.
The optimum pH range is between 7.0 and 7.4. Although growth can occur at pH values of 6 to 9, it does so at much reduced rates (see Figures 1 and 2). It is also quite likely that undesirable forms of organisms will form at these ranges and cause bulking problems. The optimal pH for nitrification is 8.0, with nitrification limited below pH 6.0.
Oxygen uptake is optimal at a 7.0 to 7.4 pH. Biochemical oxygen demand removal efficiency also decreases as pH moves outside this optimum range.
Mary Evans is a regional account manager for Premier Magnesia (Flint, Texas). She is a past president of the Water Environment Association of Texas and is the laboratory event coordinator of the WEF Operations Challenge Committee. Gary Sober is the vice president of technology for Byo-Gon Inc. (Chandler, Texas).

Please Note: The information provided in this article is designed to be educational. It is not intended to provide any type of professional advice including without limitation legal, accounting, or engineering. Your use of the information provided here is voluntary and should be based on your own evaluation and analysis of its accuracy, appropriateness for your use, and any potential risks of using the information. The Water Environment Federation (WEF), author and the publisher of this article assume no liability of any kind with respect to the accuracy or completeness of the contents and specifically disclaim any implied warranties of merchantability or fitness of use for a particular purpose. Any references included are provided for informational purposes only and do not constitute endorsement of any sources.
mizyeh 目前離線   回覆時引用此篇文章
舊 2017-11-24, 00:24   只顯示此回覆者文章   #2
rickpeng 的頭像
小名 : Rick
居住地 : 台灣新竹
魚缸尺寸 : 3尺底濾 300L
系統類別 : 實驗系統
生物類別 : 亂養缸
發文總數 : 257
註冊 : 2016-09-20
造訪 : 今天 20:24

從我的iPhone使用Tapatalk 發送
rickpeng 目前線上   回覆時引用此篇文章
舊 2017-11-24, 02:32   只顯示此回覆者文章   #3
小名 : 岳
發文總數 : 1,619
註冊 : 2012-12-18
造訪 : 2019-01-10 09:33
深海怪魚﹣蒐集 奇特怪魚﹣(蒐集)
女人的衣櫥、男人的魚缸 ;原來購物是漸進式的癮
s2s2 目前離線   回覆時引用此篇文章
舊 2017-11-24, 06:13   只顯示此回覆者文章   #4
Elton 的頭像
小名 : 老王不賣瓜
居住地 : 桃園
魚缸尺寸 : 128*106*60
系統類別 : 能活的系統
生物類別 : Great Barrier Reef 有的我都要
發文總數 : 8,593
註冊 : 2011-11-02
造訪 : 今天 20:13
海是生命的母親 珍惜資源 愛護海洋
Elton 目前線上   回覆時引用此篇文章
舊 2017-11-24, 06:31   只顯示此回覆者文章   #5
小名 : surfer
居住地 : Taoyuan
魚缸尺寸 : LPS + SPS Re-starter
系統類別 : AF
生物類別 : LPS + SPS
發文總數 : 2,648
註冊 : 2006-08-07
造訪 : 2018-01-06 18:32
感謝分享 ... 不讓水偏酸 (靠 kH as pH buffer) 應該是最基本的
atlas 目前離線   回覆時引用此篇文章
舊 2017-11-24, 10:21   只顯示此回覆者文章   #6
居住地 : 台中市
發文總數 : 125
註冊 : 2016-08-22
造訪 : 今天 19:49
huangKevin 目前離線   回覆時引用此篇文章
舊 2017-11-24, 10:30   只顯示此回覆者文章   #7
小名 : 扁魚
居住地 : 高雄人在新竹
魚缸尺寸 : 3呎
系統類別 : KZ+bio
發文總數 : 1,561
註冊 : 2005-03-25
造訪 : 今天 11:47


但還真不知道缺乏的情況下 會造成多麼劇烈的影響


所有系統都是這樣的,建康的系統底下如果KH過低 或是 "KH不消耗<<這點很重要"

3尺SPS屏風缸 Since 2015
ab333647 目前離線   回覆時引用此篇文章
舊 2017-11-24, 10:31   只顯示此回覆者文章   #8
小名 : 安A(拉瑪客)
居住地 : 台灣
魚缸尺寸 : 0.1~10米
系統類別 : 綜合多樣性生態維生系統
生物類別 : 常見海洋觀賞生物
發文總數 : 1,749
註冊 : 2011-11-30
造訪 : 今天 19:51

LMKALAN 目前離線   回覆時引用此篇文章
舊 2017-11-24, 16:51   只顯示此回覆者文章   #9
bbbabab 的頭像
小名 : 小益
居住地 : 高雄
魚缸尺寸 : 3x2x2
生物類別 : FO
發文總數 : 2,045
註冊 : 2007-06-03
造訪 : 2018-12-28 09:41

2NH3 + 4O2 --> 2HNO3 + 2H2O

HNO3 + HCO3- --> H2O + CO2 + NO3- (消耗KH)


6 NO3- + 5CH3OH --> 3N2 + 5CO2 + 7H2O + 6OH- (又把KH吐回來了)


bbbabab 目前離線   回覆時引用此篇文章
舊 2017-11-24, 17:01   只顯示此回覆者文章   #10
Jschen 的頭像
小名 : Jschen
居住地 : 台北-板橋(樹林)
魚缸尺寸 : 1.5尺
系統類別 : Lps+FO
生物類別 : 珊瑚,魚
發文總數 : 826
註冊 : 2014-12-22
造訪 : 今天 12:34
作者: bbbabab 查看文章

2NH3 + 4O2 --> 2HNO3 + 2H2O

HNO3 + HCO3- --> H2O + CO2 + NO3- (消耗KH)


6 NO3- + 5CH3OH --> 3N2 + 5CO2 + 7H2O + 6OH- (又把KH吐回來了)


請問我之前缸子No3->0 KH在不換水及補水下KH 一周會飆高2-3 是否與此有關(我有補類似吃No3的菌)
Jschen 目前離線   回覆時引用此篇文章
舊 2017-11-24, 22:15   只顯示此回覆者文章   #11
發文總數 : 137
註冊 : 2016-02-24
造訪 : 今天 20:23
keep_happy 目前線上   回覆時引用此篇文章



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