JP2003024717A - Pretreatment apparatus for slow filtration - Google Patents
Pretreatment apparatus for slow filtrationInfo
- Publication number
- JP2003024717A JP2003024717A JP2001216066A JP2001216066A JP2003024717A JP 2003024717 A JP2003024717 A JP 2003024717A JP 2001216066 A JP2001216066 A JP 2001216066A JP 2001216066 A JP2001216066 A JP 2001216066A JP 2003024717 A JP2003024717 A JP 2003024717A
- Authority
- JP
- Japan
- Prior art keywords
- layer
- raw water
- filtration
- tank
- water
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/10—Biological treatment of water, waste water, or sewage
Landscapes
- Biological Treatment Of Waste Water (AREA)
- Filtration Of Liquid (AREA)
Abstract
Description
【発明の詳細な説明】
【０００１】
【発明の属する技術分野】本発明は緩速濾過水槽に供給
される原水から汚れを取り除くための緩速濾過用前処理
装置に関するものである。
【０００２】
【従来の技術】現在、河川水などを原水として利用して
大量の飲料水を速い速度で生産するために急速濾過装置
が広く用いられている。この急速濾過装置はこの言葉通
り、原水を急速に濾過するために、塩素などの薬品を使
用することから、処理された水は薬品臭く、また水源か
ら取り入れた原水に含まれる物質と反応して発癌性物質
が生成されるなどの問題も生じている。そこで、濾過速
度が遅いが、飲料水として安全な緩速濾過装置が見直さ
れつつある。
【０００３】緩速濾過装置は濾過水槽の中に設けた複数
段の砂の層および砂利の層に原水を通して濾過する仕組
みとなっており、砂の表面に形成された微生物の濾過膜
により一般細菌から大腸菌などの各種病原菌類を始め、
鉄、マンガン、アンモニアなどを取り除き、水質検査基
準値をクリアーすることができ、薬品を使う急速濾過装
置に比べて安全な飲料水を作ることができることは周知
の事実である。
【０００４】しかしながら、この緩速濾過装置にあって
濾過水槽の中に設けた複数段の砂の層や砂利の層を通過
させて処理される原水に粘土や土壌、プランクトンなど
が混入して原水の濁度が高い場合、砂に汚れが沢山付着
することにより目詰まりを起こし、微生物処理に影響を
及ぼし、短期間ごとに濾過水槽の中に設けた砂の層や砂
利の層を洗浄しなければならず、緩速濾過装置を長期に
亘って連続運転させることが不可能であり、作業効率が
悪いという問題があった。
【０００５】
【発明が解決しようとする課題】本発明はこのような課
題を解決するもので、汚れがひどい原水を緩速濾過水槽
に供給する前に原水から汚れを効率良く取り除くことが
できる緩速濾過用前処理装置を提供することを目的とす
るものである。
【０００６】
【課題を解決するための手段】この課題を解決するため
に本発明は、緩速濾過水槽に供給される原水から汚れを
取り除くための緩速濾過用前処理装置であって、前処理
槽の内部に下端より栗石層、砕石層、玉砂利層を順番に
積層するとともに、前記玉砂利層の上に玉砂利層よりも
粒径が小さい砂からなり上段側ほど粒径が小さくなるよ
うに積層された複数段の濾材層を設け、最上段の濾材層
の砂の粒径は０．３ｍｍ未満であってこの最上段の濾材
層の厚みを他の濾材層の厚みよりも大きくし、前処理槽
の上端に原水取り入れ口を設けるとともに、前処理槽の
下端に処理水取り出し口を設け、前記原水取り入れ口か
らの原水の供給を停止させた状態で前記処理水取り出し
口より逆流洗浄水を供給するようにしたことを要旨とす
るものである。
【０００７】この構成により、汚れがひどい原水を緩速
濾過水槽に供給する前に前処理槽によって原水から原水
に含まれる粘土や土壌、プランクトンなどの汚れを効率
良く取り除いておくことによって、緩速濾過装置の長期
連続運転が可能となる。特に、前処理槽の下端より逆流
洗浄水を供給して特に比重の小さな最上段の濾材層を攪
拌させて砂同士を衝突させ、そのときの砂同士の摩擦や
水との摩擦によって砂に付着している汚濁物質を剥離さ
せ、砂から剥離した汚濁物質を浮上させて前処理槽の外
に取り出すことにより前処理槽の洗浄を短時間で行なう
ことができる。
【０００８】
【発明の実施の形態】以下、本発明の一実施の形態につ
いて、図面に基づいて説明する。図１において、１は緩
速濾過水槽に供給される原水から汚れを取り除くための
緩速濾過用前処理槽であって、前処理槽１の内部に下端
より栗石層２、砕石層３、玉砂利層４を順番に積層する
とともに、前記玉砂利層４の上に玉砂利層４よりも粒径
が小さい砂からなり上段側ほど粒径が小さくなるように
積層された複数段の濾材層５〜１４を設けてある。そし
て、最上段の濾材層１４の砂の粒径は０．３ｍｍ未満で
あってこの最上段の濾材層１４の厚みを他の濾材層５〜
１３の厚みよりも大きくしてある。具体的には、前記栗
石層２は厚みが１５ｃｍ、砕石層３〜上から２段目の濾
材層１３の各厚みが２ｃｍであるのに対し、最上段の濾
材層１４の厚みを４０ｃｍとしている。なお、この最上
段の濾材層１４は粒径０．３ｍｍ未満の砂からなり、比
重の大小により粒径が小さい砂ほど上側に位置する。つ
まり、最上段の濾材層１４にも粒径の異なる砂の層が存
在することになる。１５は前処理槽１の上端に設けられ
た原水取り入れ口、１６はこの原水取り入れ口１５より
もやや下側に設けられた越流口である。１７は前記前処
理槽１の下端に設けられた処理水取り出し口で、前記原
水取り入れ口１５からの原水の供給を停止させた状態で
処理水取り出し口１７より逆洗用水を供給するように構
成されている。
【０００９】上記構成において、濁度の高い原水は１４
リットル／ｍｉｎ・ｍ2 程度の流速で原水取り入れ口１
５より前処理槽１の内部に供給され、前記粒径０．３ｍ
ｍ未満の砂からなる最上段の濾材層１４より濾材層１３
〜５を通過し、その後玉砂利層４、砕石層３、栗石層２
を通過して前記処理水取り出し口１７より取り出され、
前処理槽１に隣接する緩速濾過水槽に原水として供給さ
れる。原水取り入れ口１５より前処理槽１の内部に供給
される原水の汚れの殆どは前記粒径０．３ｍｍ未満の砂
からなる最上段の濾材層１４により取り除かれるのであ
るが、粒径０．３ｍｍ未満の砂からなる濾材層１４の下
に濾材層１３〜５、玉砂利層４、砕石層３、栗石層２が
設けられているのは、濾材層１４の砂が処理水取り出し
口１７より流れ出さないようにするためと、後述する逆
流洗浄水による洗浄作業時において濾材層１４に対して
逆流洗浄水を満遍なく送り込むためである。ところで、
本実施の形態において流速１４リットル／ｍｉｎ・ｍ2
程度で前処理槽１に供給される原水を処理するように構
成されているが、これは緩速濾過水槽に供給される原水
の流速の約３倍程度である。前処理槽１に供給される原
水の流速を緩速濾過水槽に供給される原水の流速よりも
速くしたのは、遅くすると前処理槽１で微生物分解を起
こし、目詰まりが発生しやすくなるためである。
【００１０】前述のように原水の汚れの殆どは粒径０．
３ｍｍ未満の砂からなる最上段の濾材層１４に付着する
のであるが、前処理槽１内の栗石層２、砕石層３、玉砂
利層４、濾材層５〜１４、特に最上段の濾材層１４の汚
れを取り除くために前処理槽１を定期的に洗浄する必要
がある。この前処理槽１、特に最上段の濾材層１４が汚
れるにつれて前処理槽１での処理速度が低下し、処理水
取り出し口１７より取り出される処理水の量が減ってく
る。これにより前処理槽１内での水面の高さが上昇する
ことになり、前記越流口１６から原水がオーバーフロー
する。この現象を確認して洗浄作業に移るのである。そ
こで、その洗浄作業について以下に説明する。
【００１１】先ず、前処理槽１に対する前記原水取り入
れ口１５からの原水の供給を停止させるとともに、前記
越流口１６を開いたた状態で前記処理水取り出し口１７
より前処理槽１に逆流洗浄水を供給する。前処理槽１の
下端より供給された逆流洗浄水は栗石層２、砕石層３、
玉砂利層４、濾材層５〜１４を通って前処理槽１内で上
昇し、特に比重の小さな最上段の濾材層１４を攪拌させ
て砂同士を衝突させ、そのときの砂同士の摩擦や水との
摩擦によって砂に付着している汚濁物質の剥離が生じ
る。砂から剥離した汚濁物質は浮上して越流口１６の高
さでオーバーフローする水とともに越流口１６に吸い込
まれる。このような洗浄作業を持続して濾材層１４上方
の前処理槽１上部の水の濁りがなくなったことを確認し
た後、洗浄作業を停止する。なお、洗浄作業に用いる逆
流洗浄水の流速は１７０リットル／ｍｉｎ・ｍ2 〜２５
０リットル／ｍｉｎ・ｍ2 の範囲であれば良いが、その
中でも２００リットル／ｍｉｎ・ｍ2 程度が最適であ
り、遅すぎると汚濁物質の剥離が遅れ、洗浄作業に時間
がかかることになり、また速すぎると砂も一緒に越流口
１６より流出するおそれがある。
【００１２】ところで、洗浄作業時において前処理槽１
上部の水の濁り状態を確認するために図面では示されて
いないが、前処理槽１の上部に透明な確認窓が形成され
ている。
【００１３】
【発明の効果】以上のように本発明によれば、汚れがひ
どい原水を緩速濾過水槽に供給する前に前処理槽によっ
て原水から原水に含まれる粘土や土壌、プランクトンな
どの汚れを効率良く取り除いておくことによって、緩速
濾過装置の長期連続運転が可能となる。特に、前処理槽
の下端より逆流洗浄水を供給して特に比重の小さな最上
段の濾材層を攪拌させて砂同士を衝突させ、そのときの
砂同士の摩擦や水との摩擦によって砂に付着している汚
濁物質を剥離させ、砂から剥離した汚濁物質を浮上させ
て前処理槽の外に取り出すことにより前処理槽の洗浄を
短時間で行なうことができる。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slow filtration pretreatment device for removing dirt from raw water supplied to a slow filtration water tank. [0002] At present, rapid filtration devices are widely used to produce a large amount of drinking water at a high speed using river water or the like as raw water. This rapid filtration device uses chemicals such as chlorine to rapidly filter raw water, as it implies, so the treated water has a chemical odor and reacts with the substances contained in the raw water taken from the water source. Problems such as generation of carcinogenic substances have also occurred. Thus, slow filtration devices that have low filtration speeds but are safe as drinking water are being reviewed. [0003] The slow filtration device has a mechanism of filtering raw water through a plurality of layers of sand and gravel provided in a filtration water tank, and a general bacteria is formed by a filtration membrane of microorganisms formed on the surface of sand. From various pathogenic fungi such as E. coli,
It is a well-known fact that iron, manganese, ammonia, etc. can be removed, water quality inspection standards can be cleared, and safe drinking water can be produced as compared to a rapid filtration device using chemicals. However, in this slow filtration apparatus, clay, soil, plankton, and the like are mixed into raw water that is processed by passing through a plurality of layers of sand or gravel provided in a filtration water tank. If the turbidity of the sand is high, the sand will become clogged with a lot of dirt, causing clogging, affecting microbial treatment, and the sand layer and gravel layer installed in the filtration tank must be washed every short period of time. Therefore, it is impossible to operate the slow filtration device continuously for a long period of time, and there is a problem that the working efficiency is poor. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a dirt can be efficiently removed from raw water before supplying the dirt-rich raw water to a slow filtration water tank. It is an object of the present invention to provide a pretreatment device for rapid filtration. [0006] In order to solve this problem, the present invention is a slow filtration pretreatment device for removing dirt from raw water supplied to a slow filtration water tank, comprising: Inside the treatment tank, a stone bed layer, a crushed stone layer, and a gravel layer are sequentially stacked from the lower end, and a layer of sand having a smaller particle size than that of the gravel layer is formed on the gravel layer so that the particle size becomes smaller toward the upper side. The uppermost filter medium layer has a sand particle size of less than 0.3 mm, and the thickness of the uppermost filter medium layer is made larger than the thickness of the other filter medium layers. A raw water intake port is provided at the upper end of the tank, and a treated water outlet port is provided at the lower end of the pretreatment tank, and backflow washing water is supplied from the treated water outlet port while supply of raw water from the raw water intake port is stopped. The point is that you tried to do It is. [0007] According to this configuration, before the raw water having heavy dirt is supplied to the slow filtration water tank, the pretreatment tank efficiently removes dirt such as clay, soil, and plankton contained in the raw water from the raw water. Long-term continuous operation of the filtration device becomes possible. In particular, backwash water is supplied from the lower end of the pretreatment tank to agitate the uppermost filter medium layer, which has a particularly low specific gravity, so that the sands collide with each other and adhere to the sand due to friction between the sand and friction with water at that time. The pretreatment tank can be cleaned in a short time by removing the contaminant that has been removed, floating the contaminant removed from the sand, and taking it out of the pretreatment tank. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a pretreatment tank for slow filtration for removing dirt from raw water supplied to a slow filtration water tank. The layers 4 are sequentially laminated, and a plurality of filter media layers 5 to 14 are formed on the gravel layer 4, which are made of sand having a smaller particle diameter than the gravel layer 4 and are laminated such that the particle size decreases toward the upper side. It is provided. The particle size of the sand in the uppermost filter medium layer 14 is less than 0.3 mm, and the thickness of this uppermost filter medium layer 14 is
13 is larger than the thickness. Specifically, the chestnut stone layer 2 has a thickness of 15 cm, and the crushed stone layers 3 to the second-stage filter medium layer 13 from above each have a thickness of 2 cm, whereas the uppermost-stage filter medium layer 14 has a thickness of 40 cm. . The uppermost filter medium layer 14 is made of sand having a particle diameter of less than 0.3 mm, and the sand having a smaller particle diameter is located on the upper side depending on the specific gravity. That is, a sand layer having a different particle size also exists in the uppermost filter medium layer 14. Reference numeral 15 denotes a raw water intake port provided at the upper end of the pretreatment tank 1, and reference numeral 16 denotes an overflow port provided slightly below the raw water intake port 15. Reference numeral 17 denotes a treated water outlet provided at the lower end of the pretreatment tank 1, which is configured to supply backwash water from the treated water outlet 17 in a state where supply of raw water from the raw water intake 15 is stopped. Have been. In the above configuration, the raw water having a high turbidity is 14
Raw water intake 1 at a flow rate of about 1 liter / min · m 2
5 is supplied to the inside of the pretreatment tank 1 and the particle diameter is 0.3 m
m from the uppermost filter medium layer 14 made of sand
~ 5, then the gravel layer 4, crushed stone layer 3, kuriishi layer 2
Through the treated water outlet 17 and
The raw water is supplied to a slow filtration water tank adjacent to the pretreatment tank 1. Most of the dirt of the raw water supplied from the raw water intake 15 into the pretreatment tank 1 is removed by the uppermost filter medium layer 14 made of sand having a particle diameter of less than 0.3 mm. The filter medium layers 13-5, the pebble layer 4, the crushed stone layer 3, and the rubble stone layer 2 are provided below the filter medium layer 14 made of less than three pieces of sand, because the sand of the filter medium layer 14 flows out from the treated water outlet 17. This is to prevent the backwash water from being evenly supplied to the filter medium layer 14 during the washing operation using the backwash water described below. by the way,
In this embodiment, the flow rate is 14 liter / min · m 2
Although the raw water supplied to the pretreatment tank 1 is configured to be treated to a degree, this is about three times the flow rate of the raw water supplied to the slow filtration water tank. The reason why the flow rate of the raw water supplied to the pretreatment tank 1 was set to be higher than the flow rate of the raw water supplied to the slow filtration water tank is that if the flow rate is reduced, microbial decomposition occurs in the pretreatment tank 1 and clogging is likely to occur. It is. As described above, most of the dirt in the raw water has a particle size of 0.3.
It adheres to the uppermost filter medium layer 14 made of sand having a size of less than 3 mm, but the stone layer 2, the crushed stone layer 3, the gravel layer 4, and the filter medium layers 5 to 14 in the pretreatment tank 1, especially the uppermost filter medium layer 14 It is necessary to periodically clean the pretreatment tank 1 in order to remove dirt. As the pretreatment tank 1, especially the uppermost filter medium layer 14 becomes contaminated, the treatment speed in the pretreatment tank 1 decreases, and the amount of treatment water taken out from the treatment water outlet 17 decreases. As a result, the height of the water surface in the pretreatment tank 1 increases, and the raw water overflows from the overflow port 16. After confirming this phenomenon, the cleaning operation is started. Therefore, the cleaning operation will be described below. First, the supply of raw water from the raw water intake port 15 to the pretreatment tank 1 is stopped, and the treated water outlet port 17 is opened with the overflow port 16 opened.
The backwash water is supplied to the pretreatment tank 1. The backwashing water supplied from the lower end of the pretreatment tank 1 is composed of
It rises in the pretreatment tank 1 through the gravel layer 4 and the filter medium layers 5 to 14, and in particular, agitates the uppermost filter medium layer 14 having a small specific gravity to cause the sand to collide with each other. As a result, the contaminants adhering to the sand are peeled off. The pollutants separated from the sand float up and are sucked into the overflow 16 together with water overflowing at the level of the overflow 16. After confirming that the turbidity of water in the upper part of the pretreatment tank 1 above the filter medium layer 14 has been maintained by continuing such a washing operation, the washing operation is stopped. The flow rate of the backwash water used for the washing operation is 170 liter / min · m 2 -25
A range of 0 liter / min · m 2 is sufficient, but among them, about 200 liter / min · m 2 is optimal. If it is too slow, separation of pollutants is delayed, and a long time is required for cleaning work. If the speed is too high, the sand may flow out from the overflow port 16 together. By the way, during the cleaning operation, the pretreatment tank 1
Although not shown in the drawings to confirm the turbidity of the water in the upper part, a transparent confirmation window is formed in the upper part of the pretreatment tank 1. As described above, according to the present invention, before supplying raw water with heavy dirt to the slow-filtration water tank, dirt such as clay, soil and plankton contained in raw water from raw water is supplied by the pretreatment tank. , The long-term continuous operation of the slow filtration device becomes possible. In particular, backwash water is supplied from the lower end of the pretreatment tank to agitate the uppermost filter medium layer, which has a particularly low specific gravity, so that the sands collide with each other and adhere to the sand due to friction between the sand and friction with water at that time. The pretreatment tank can be cleaned in a short time by removing the contaminant that has been removed, floating the contaminant removed from the sand, and taking it out of the pretreatment tank.
【図面の簡単な説明】
【図1】本発明の一実施の形態における緩速濾過用前処
理装置の断面図である。
【符号の説明】
１ 前処理槽
２ 栗石層
３ 砕石層
４ 玉砂利層
５〜１４ 濾材層
１５ 原水取り入れ口
１６ 越流口
１７ 処理水取り出し口BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a slow filtration pretreatment device according to an embodiment of the present invention. [Description of Signs] 1 Pretreatment tank 2 Kuriishi layer 3 Crushed stone layer 4 Cobbled layer 5-14 Filter media layer 15 Raw water intake 16 Overflow opening 17 Treated water outlet
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｃ０２Ｆ 3/06 ──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. 7 Identification symbol FI Theme coat ゛ (Reference) C02F 3/06
Claims (1)
取り除くための緩速濾過用前処理装置であって、前処理
槽の内部に下端より栗石層、砕石層、玉砂利層を順番に
積層するとともに、前記玉砂利層の上に玉砂利層よりも
粒径が小さい砂からなり上段側ほど粒径が小さくなるよ
うに積層された複数段の濾材層を設け、最上段の濾材層
の砂の粒径は０．３ｍｍ未満であってこの最上段の濾材
層の厚みを他の濾材層の厚みよりも大きくし、前処理槽
の上端に原水取り入れ口を設けるとともに、前処理槽の
下端に処理水取り出し口を設け、前記原水取り入れ口か
らの原水の供給を停止させた状態で前記処理水取り出し
口より逆流洗浄水を供給するようにしたことを特徴とす
る緩速濾過用前処理装置。Claims 1. A slow-filtration pretreatment device for removing dirt from raw water supplied to a slow-filtration water tank, wherein a lithic stone layer and a crushed stone layer are formed inside the pretreatment tank from the lower end. A plurality of layers of filter media layer laminated in order, and a plurality of filter media layers formed of sand having a smaller particle size than that of the gravel layer and having a smaller particle size toward the upper stage side are provided on the gravel layer, The sand size of the filter medium layer is less than 0.3 mm, the thickness of the uppermost filter medium layer is larger than the thickness of the other filter medium layers, and a raw water intake port is provided at the upper end of the pretreatment tank. A slow-flow filter provided with a treated water outlet at the lower end of the treatment tank and supplying backwash water from the treated water outlet in a state where supply of raw water from the raw water intake is stopped. Pretreatment equipment.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001216066A JP3681345B2 (en) | 2001-07-17 | 2001-07-17 | Pretreatment device for slow filtration |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001216066A JP3681345B2 (en) | 2001-07-17 | 2001-07-17 | Pretreatment device for slow filtration |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2003024717A true JP2003024717A (en) | 2003-01-28 |
| JP3681345B2 JP3681345B2 (en) | 2005-08-10 |
Family
ID=19050590
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2001216066A Expired - Fee Related JP3681345B2 (en) | 2001-07-17 | 2001-07-17 | Pretreatment device for slow filtration |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3681345B2 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008272711A (en) * | 2007-05-07 | 2008-11-13 | Itsuo Morizaki | Water clarification method and clarification apparatus |
| JP2009291752A (en) * | 2008-06-09 | 2009-12-17 | Koyo:Kk | Slow filtration apparatus |
| CN105293604A (en) * | 2015-12-03 | 2016-02-03 | 青海师范大学 | Slow sand filtering water treatment device and slow sand filtering water treatment system |
-
2001
- 2001-07-17 JP JP2001216066A patent/JP3681345B2/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008272711A (en) * | 2007-05-07 | 2008-11-13 | Itsuo Morizaki | Water clarification method and clarification apparatus |
| JP2009291752A (en) * | 2008-06-09 | 2009-12-17 | Koyo:Kk | Slow filtration apparatus |
| CN105293604A (en) * | 2015-12-03 | 2016-02-03 | 青海师范大学 | Slow sand filtering water treatment device and slow sand filtering water treatment system |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3681345B2 (en) | 2005-08-10 |
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