中文字幕理伦午夜福利片_成人黄色在线免费观看_欧美黑人巨大videos极品_国产精品无码久久久久久_少妇人妻真实偷人精品视频_av在线高清观看_欧美黑人狂躁日本寡妇_国产精品久久久久久久久久免费看_大伊香蕉精品视频在线天堂_国产成人av片在线观看_av中文字幕不卡_丰满少妇大力进入av_亚洲欧美国产免费综合视频_玩弄人妻奶水无码av在线_精品无码一区二区三区电影_欧美丰满一区二区免费视频_国产亚洲欧洲综合5388_人人妻人人添人人爽日韩欧美_无码日韩人妻av一区免费_欧美激情网站

關于水處理知識的31個問答(下)

2020-04-12  來自: 衡美水處理公眾平臺 瀏覽次數:1060


如何發展環保事業?

衡美水處理為您介紹一位圈內行家的經典筆記,供大家充電學習,一項環境保護的***知識——關于水處理31個問答。

水處理知識

二十一、濃水循環頻繁自動倒極系統是如何實現的?其意義是什么?

答:在當前的水處理行業中,濃水循環頻繁自動倒極系統是以可編程控制器為控制核心,以系統產水工藝運行時間為控制函數,利用電動或氣動直通閥門、三通閥門來定時切換濃淡水的水流方向,使淡水始終流入產水箱,而濃水固定排入濃水循環箱。

在水資源日益匱乏的今天,濃水循環頻繁自動倒極系統具有深遠的意義,一、該系統的水回收率較高可達到80%(視進水水質而定),在一些大型水處理系統中節水的效果非常明顯。第二、該系統的造價比較低,對系統進水水質的要求比較低,容易推廣(在一些對回收率要求較高而又不能夠投入較多資金的企業或廠礦的水處理項目中比較有競爭力)。

二十二、水處理系統工程中需要那些種類水泵?不同廠家的水泵該如何選型

答:水處理系統工程中大致需要普通型泵、增壓型泵、防腐蝕型泵。普通型泵一般選用IS 型鑄鐵水泵;增壓型水泵一般選用不銹鋼水泵如丹麥格蘭夫進口高壓泵(根據具體情況而定);防腐蝕型水泵一般選用IH 型化工泵或工程朔料水泵。

不同廠家的水泵型號都有所不同,首先根據系統的工藝要求選擇水泵的流量;其次根據工藝要求選擇水泵的揚程(1公斤約等于10 米揚程,1MPa 約等于10 公斤);再次根據工藝要求來選擇水泵的材質(主要是指水泵泵頭的材質);根據各種水泵的耗電量來選擇即能達到工藝要求又能節省系統能耗的水泵。

二***錘現象是什么?如何解決這一問題?

答:“水錘”是由于壓力容器中混有空氣,在啟動裝置的時候沒有采用***的手段來排除容器中的空氣,以至于高壓水流混雜著空氣向容器內運動時產生劇烈的震動,嚴重時會將膜元件擊的粉碎,帶來不可恢復的損失。

“防范在先、預防為主”, 如何防止產生“水錘”現象就顯得相當重要。一般采取的措施有:

1、高壓泵采用軟啟動方式避免,如降壓啟動、變頻調速啟動、帶自動控制器的串電阻啟動。

2、在操作方式上避免,如在啟動時將進口閥門關閉或關小,然后緩慢打開閥門,直到達到系統工作壓力時為止。

3、利用控制防止避免,如用 PLC 控制一電動慢開門,在幾十秒的時間內打開閥門。

4、利用安裝工藝防止,如在濃水排放口設一回流管道,使得管道的高點超過反滲透裝置中的壓力容器,這樣在裝置停止運行時就會在壓力容器內存滿水。 以上幾點是工程應用中常采用的措施,可都采納也可根據實際情況采用幾點,值得注意的是不論哪一個工程第 4 點是***的。

二十四、反滲透濃水排放管為什么***比裝置高出一點?

答:濃水排放閥在反滲透運行時是始終打開的,這樣當反滲透裝置停止運行時,如果排放管的高點低于壓力容器的高點時就會產生“虹吸”現象,壓力容器中的水會由于自重通過濃水排放管流出反滲透裝置,在壓力容器中混入了空氣,一是容易引起水錘現象的產生,二是停機運行時空氣中的氧氣會對反滲透膜元件產生或多或少的氧化作用,影響膜元件的使用壽命

二十五、電滲析、反滲透的進水指標

答:電滲析的進水指標有:

溫度范圍:4-40℃ 含鐵、錳量:Fe0.3mg/lMn0.1mg/l

濁度:小于 0.3mg/l(對 0.9mm 厚的隔板) SDI 約等于 0

游離氯:CL0.3mg-0.5mg/l

反滲透的進水指標有:

含鐵量:Fe1mg/l

游離氯:CL0.1mg

SDI:小于 4 溫度范圍:5-45℃ 濁度:小于 1NTU

二十六、機械過濾器除鐵除錳過濾器、除二氧化碳器進出水指標?

答:機械過濾器的進水懸浮物20mg/l,出水懸浮物≤5mg/l。 除鐵除錳過濾器的進水含鐵量≤30mg/l,出水含鐵量≤0.3mg/l。 除二氧化碳器進水二氧化碳含量≤330mg/l,出水二氧化碳含量≤5mg/l

二十七、如何控制濃差極化現象?

答:

1嚴格控制操作電流,是電滲析在低于極限電流密度的條件下運行。

2強化電滲析隔室中的傳遞過程,例如采用湍流效果好的隔網,高溫電滲析。

3采用定期酸洗,加入防垢劑,倒換電極等措施消除濃差極化現象產生的沉淀。

4可采用適當的預處理來改善系統進水水質。

二十八、紫外線殺菌器的特點是什么?

答:紫外線殺菌器的特點如下:

1紫外線殺菌速度快、效率***果好。

2、紫外線照射不會改變水的物理、化學性質,對純水不會帶如附加物所引入的污染

3、能適用于各種水的流量下使用,操作簡單,使用方便,只需定期地清洗石英玻璃管套。

4、體積小,輕便、耗電低、壽命長。

二十九、影響紫外線殺菌器效果的因素和注意的事項是什么?

答:影響紫外線殺菌效果的因素是紫外線的強度、紫外線光譜的波長和照射時間。

在使用紫外線殺菌器時應注意的事項為:

安裝位置:紫外線安裝的位置離使用點越近越好,但也應留有從一端裝進或抽出石英管套和更換燈管的操作空間。

流量:在同一殺菌器內,當紫外線的輻射能量固定,水中細菌含量變化不大時通過殺菌器的水流量大小對殺菌效果有顯著的影響。

水的物理化學性質:水的色度、濁度、總鐵含量對紫外線都有不同程度的吸收, 其結果使殺菌的效果降低。

燈管功率:燈管的點燃功率對殺菌效率影響很大。

燈管周圍的介質溫度:紫外線燈管輻射光譜能量與燈管管壁的溫度有關。

石英管套:適應管套的質量和壁厚與紫外線的透過率有關,石英管套的純度高,效率好。

水層厚度:水層厚度對殺菌效果有很大的關系。

三十、臭氧殺菌器的特點是什么?

答:臭氧是水處理中很有效的殺菌劑,只有游離氯才能和臭氧的殺菌能力相比。

優點:用臭氧消毒的優點是其殺菌效率高,即使對于如病毒和囊孢等抵抗性強的微生物,它也是很有效的消毒劑。它可以減少給水的嗅、味和色度,并且在分解時它剩余物質是溶解氧。另外,臭氧的殺菌能力不受 PH 值變化和氨的影響。

缺點:用臭氧消毒也有不利的一面,因為***用電產生臭氧,并且不能儲備,在遇到水質和水量變化時,對臭氧的需用量難于及時調整。經驗證明臭氧適用于用水量低而用水量穩定的水廠;此外臭氧雖強氧化劑,但其氧化能力是有選擇性的,并不是普遍產生氧化作用,像乙醇這種容易被氧化的物質卻不容易和臭氧作用。

三十一、水質分析中水樣采集應注意什么問題?

答:水質分析中水樣采集應注意以下幾個問題:

1、采樣應具有代表性,即所采取水樣能代表整個水體的水質。

2、水樣的水質應在采用與分析之間應該穩定不變或無明顯的變化。 取樣量應為檢測項目需樣量的 4-5 倍,以保證重復分析和復檢的水樣量,取樣量應以保證分析的準確度與精度的要求為準。

3、盡量縮短水樣和取樣設備的接觸時間,水樣流經管線應采取高線性流速,如果采用時需要連接管路和閥門等中間流路,應特別注意這一中間環節的污染問題, 其材質與清洗的要求應與采用容器一致。

4、現場測試的項目,如 PH 值、溶解氧、堿度、CO2、亞鐵、氨態氮、余氯等含量,應盡量縮短取樣至分析餓時間間隔,且應盡量采用在線分析檢測。

5、應備有采用記錄并在采樣容器上貼標簽,注明采用名稱、時間、地點、溫度、采樣量、采用容器及采樣人等。

衡美水處理專注水處理設備生產十五年,為您量身定制水處理解決方案


衡水市衡美水處理設備有限公司,專營 淺層砂過濾器 過濾器 全自動加藥裝置 原水處理設備 等業務,有意向的客戶請咨詢我們,聯系電話:0318-2987119

CopyRight ? 版權所有: 衡水市衡美水處理設備有限公司 技術支持:衡水航宇 網站地圖 XML

本站關鍵字: 反滲透設備


掃一掃訪問移動端
主站蜘蛛池模板: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |