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Guguwar ƙura tana haifar da babbar barazana ga ƙasashe da yawa a duniya saboda mummunan tasirin da take yi wa noma, lafiyar ɗan adam, hanyoyin sufuri da kayayyakin more rayuwa. Sakamakon haka, ana ɗaukar zaizayar iska a matsayin matsala ta duniya. Ɗaya daga cikin hanyoyin da ba su da illa ga muhalli don rage zaizayar iska shine amfani da hazo mai haifar da ƙwayoyin cuta (MICP). Duk da haka, abubuwan da ke haifar da MICP mai lalata urea, kamar ammonia, ba su da kyau idan aka samar da su da yawa. Wannan binciken ya gabatar da tsari biyu na ƙwayoyin cuta na calcium formate don lalata MICP ba tare da samar da urea ba kuma ya kwatanta aikinsu da tsari biyu na ƙwayoyin cuta na calcium acetate waɗanda ba sa samar da ammonia. Kwayoyin cuta da aka yi la'akari da su sune Bacillus subtilis da Bacillus amyloliquefaciens. Da farko, an tantance ƙimar abubuwan da suka dace na abubuwan da ke sarrafa samuwar CaCO3. Daga nan aka gudanar da gwaje-gwajen ramin iska akan samfuran dune na yashi da aka yi wa magani da ingantaccen tsari, kuma an auna juriyar zaizayar iska, saurin yankewa, da juriyar jefa yashi. An kimanta allomorphs na Calcium carbonate (CaCO3) ta amfani da na'urar hangen nesa, na'urar daukar hoton electron microscopy (SEM), da kuma nazarin diffraction na X-ray. Tsarin da aka yi amfani da shi bisa tsarin calcium sun yi aiki mafi kyau fiye da tsarin acetate dangane da samuwar calcium carbonate. Bugu da ƙari, B. subtilis ya samar da ƙarin calcium carbonate fiye da B. amyloliquefaciens. Hotunan SEM sun nuna a sarari cewa ƙwayoyin cuta masu aiki da marasa aiki suna ɗaurewa da kuma buga ƙwayoyin cuta masu aiki akan calcium carbonate wanda sedimentation ke haifarwa. Duk tsarin sun rage zaizayar iska sosai.
Zaftarewar iska ta daɗe ana gane ta a matsayin babbar matsala da ke fuskantar yankunan busassu da rabin-hamada kamar kudu maso yammacin Amurka, yammacin China, Afirka ta Sahara, da kuma mafi yawan Gabas ta Tsakiya1. Rashin ruwan sama a yanayin busassu da tsananin hamada ya canza manyan sassan waɗannan yankuna zuwa hamada, tuddai na yashi, da kuma ƙasashen da ba a noma ba. Ci gaba da zaftarewar iska yana haifar da barazanar muhalli ga ababen more rayuwa kamar hanyoyin sufuri, ƙasar noma, da ƙasar masana'antu, wanda ke haifar da mummunan yanayin rayuwa da tsadar ci gaban birane a waɗannan yankuna2,3,4. Abu mafi mahimmanci, zaftarewar iska ba wai kawai tana shafar wurin da take faruwa ba, har ma tana haifar da matsalolin lafiya da tattalin arziki a cikin al'ummomi masu nisa yayin da take jigilar ƙwayoyin cuta ta iska zuwa yankunan da ke nesa da tushenta5,6.
Kula da zaizayar ƙasa ta kasance matsala ta duniya. Ana amfani da hanyoyi daban-daban na daidaita ƙasa don magance zaizayar ƙasa. Waɗannan hanyoyin sun haɗa da kayan aiki kamar amfani da ruwa7, haƙoran mai8, biopolymers5, haƙoran carbonate da ƙwayoyin cuta ke haifarwa (MICP)9,10,11,12 da haƙoran carbonate da enzyme ke haifarwa (EICP)1. Jika ƙasa hanya ce ta yau da kullun ta rage ƙura a cikin filin. Duk da haka, saurin ƙafewarta yana sa wannan hanyar ta kasance mai ƙarancin tasiri a yankuna busassu da rabin-hatsi1. Aiwatar da mahaɗan haƙoran mai yana ƙara haɗin yashi da gogayya tsakanin ɓangarorin biyu. Haƙƙinsu na haɗa yashi tare; duk da haka, haƙoran mai kuma suna haifar da wasu matsaloli; launinsu mai duhu yana ƙara shaƙar zafi kuma yana haifar da mutuwar shuke-shuke da ƙananan halittu. Ƙamshinsu da hayakinsu na iya haifar da matsalolin numfashi, kuma mafi mahimmanci, babban farashinsu wani cikas ne. Biopolymers suna ɗaya daga cikin hanyoyin da aka gabatar kwanan nan don rage zaizayar ƙasa; ana cire su daga tushen halitta kamar shuke-shuke, dabbobi da ƙwayoyin cuta. Xanthan gum, guar gum, chitosan da gellan gum sune biopolymers da aka fi amfani da su a aikace-aikacen injiniyanci5. Duk da haka, biopolymers masu narkewa cikin ruwa na iya rasa ƙarfi da kuma fitar da ruwa daga ƙasa lokacin da aka fallasa su ga ruwa13,14. An nuna cewa EICP hanya ce mai tasiri ta rage ƙura don aikace-aikace iri-iri, gami da hanyoyi marasa shimfidawa, tafkunan wutsiya da wuraren gini. Duk da cewa sakamakonsa yana da ban sha'awa, dole ne a yi la'akari da wasu matsaloli, kamar farashi da rashin wuraren nucleation (wanda ke hanzarta samuwar lu'ulu'u na CaCO3 da kuma ruwan sama15,16).
An fara bayyana MICP a ƙarshen ƙarni na 19 ta Murray da Irwin (1890) da Steinmann (1901) a cikin bincikensu kan lalacewar urea ta hanyar ƙwayoyin cuta na ruwa17. MICP wani tsari ne na halitta wanda ya ƙunshi nau'ikan ayyukan ƙwayoyin cuta da hanyoyin sinadarai inda sinadarin calcium carbonate ke haifar da amsawar ions na carbonate daga metabolites na ƙwayoyin cuta tare da ions na calcium a cikin muhalli18,19. MICP wanda ya shafi zagayowar nitrogen mai lalata urea (MICP mai lalata urea) shine nau'in ruwan sama mai yawan ƙwayoyin cuta, wanda urease da ƙwayoyin cuta ke samarwa ke haifar da hydrolysis na urea20,21,22,23,24,25,26,27 kamar haka:
A cikin MICP wanda ya shafi zagayowar carbon na iskar shaka ta gishirin halitta (MICP ba tare da nau'in lalata urea ba), ƙwayoyin cuta masu heterotrophic suna amfani da gishirin halitta kamar acetate, lactate, citrate, succinate, oxalate, malate da glyoxylate a matsayin tushen makamashi don samar da ma'adanai na carbon28. A gaban calcium lactate a matsayin tushen carbon da ions na calcium, an nuna amsawar sinadarai na samuwar calcium carbonate a cikin lissafi (5).
A cikin tsarin MICP, ƙwayoyin cuta suna samar da wuraren nucleation waɗanda suke da mahimmanci musamman don hazo na calcium carbonate; saman ƙwayoyin cuta yana da caji mara kyau kuma yana iya aiki azaman mai sha don divalent cations kamar calcium ions. Ta hanyar shaye ions na calcium akan ƙwayoyin cuta, lokacin da yawan carbonate ion ya isa, cations na calcium da carbonate anions suna amsawa kuma calcium carbonate yana hawowa akan saman ƙwayoyin cuta29,30. Ana iya taƙaita tsarin kamar haka31,32:
Ana iya raba lu'ulu'u na calcium carbonate da aka samar ta hanyar halitta zuwa nau'i uku: calcite, vaterite, da aragonite. Daga cikinsu, calcite da vaterite sune allomorphs na calcium carbonate da aka fi samu ta hanyar ƙwayoyin cuta33,34. Calcite shine allomorph35 mafi ƙarfi a cikin calcium carbonate. Duk da cewa an ruwaito cewa vaterite yana da ƙarfi, daga ƙarshe ya canza zuwa calcite36,37. Vaterite shine mafi yawan lu'ulu'u. Lu'ulu'u ne mai siffar hexagonal wanda ke da ƙarfin cika ramuka fiye da sauran lu'ulu'u na calcium carbonate saboda girmansa mafi girma38. MICP mai laushi da urea-ungraded na iya haifar da hazo na vaterite13,39,40,41.
Duk da cewa MICP ta nuna kyakkyawan damar daidaita ƙasa mai matsala da ƙasa mai saurin yaɗuwa daga iska42,43,44,45,46,47,48, ɗaya daga cikin abubuwan da ke haifar da hydrolysis na urea shine ammonia, wanda zai iya haifar da matsalolin lafiya masu sauƙi zuwa masu tsanani dangane da matakin fallasa49. Wannan illar ta sa amfani da wannan fasaha ta musamman ya zama abin jayayya, musamman lokacin da manyan wurare ke buƙatar a yi musu magani, kamar don rage ƙura. Bugu da ƙari, warin ammonia ba zai iya jurewa ba idan ana gudanar da aikin a cikin babban adadin aikace-aikace da kuma babban adadi, wanda zai iya shafar amfaninsa a aikace. Kodayake binciken da aka yi kwanan nan ya nuna cewa ana iya rage ammonia ions ta hanyar canza su zuwa wasu samfura kamar struvite, waɗannan hanyoyin ba sa cire ammonia ions gaba ɗaya50. Saboda haka, har yanzu akwai buƙatar bincika wasu hanyoyin magance matsalolin da ba sa samar da ammonia ions. Amfani da hanyoyin lalata ba tare da urea ba don MICP na iya samar da mafita mai yuwuwa wanda ba a bincika shi da kyau ba a cikin mahallin rage yaɗuwar iska. Fattahi et al. sun binciki lalacewar MICP mara urea ta amfani da calcium acetate da Bacillus megaterium41, yayin da Mohebbi da sauransu suka yi amfani da calcium acetate da Bacillus amyloliquefaciens9. Duk da haka, bincikensu bai yi daidai da sauran tushen calcium da ƙwayoyin cuta masu heterotrophic waɗanda a ƙarshe za su iya inganta juriya ga zaizayar iska ba. Akwai kuma rashin wallafe-wallafen da ke kwatanta hanyoyin lalata ba tare da urea ba tare da hanyoyin lalata urea a cikin rage zaizayar iska.
Bugu da ƙari, an gudanar da yawancin nazarin zaizayar iska da kuma kula da ƙura akan samfuran ƙasa masu saman lebur.1,51,52,53 Duk da haka, saman lebur ba su da yawa a yanayi kamar tuddai da ramuka. Wannan shine dalilin da ya sa tuddai masu yashi su ne mafi yawan abubuwan da ake gani a yanayin ƙasa a yankunan hamada.
Domin shawo kan kurakuran da aka ambata a sama, wannan binciken yana da nufin gabatar da sabon saitin magungunan ƙwayoyin cuta waɗanda ba sa samar da ammonia. Don wannan dalili, mun yi la'akari da hanyoyin MICP marasa urea da ke lalata su. An binciki ingancin tushen calcium guda biyu (calcium formate da calcium acetate). A gwargwadon ilimin marubutan, ba a binciki hazo na carbonate ta amfani da haɗin tushen calcium guda biyu da ƙwayoyin cuta ba (misali calcium formate-Bacillus subtilis da calcium formate-Bacillus amyloliquefaciens) a cikin binciken da suka gabata. Zaɓin waɗannan ƙwayoyin cuta ya dogara ne akan enzymes da suke samarwa waɗanda ke haɓaka iskar oxygen na calcium formate da calcium acetate don samar da hazo na microbial carbonate. Mun tsara cikakken bincike na gwaji don nemo abubuwan da suka fi dacewa kamar pH, nau'ikan ƙwayoyin cuta da tushen calcium da yawansu, rabon ƙwayoyin cuta zuwa maganin tushen calcium da lokacin warkarwa. A ƙarshe, an binciki ingancin wannan rukunin magungunan ƙwayoyin cuta wajen rage zaizayar iska ta hanyar ruwan calcium carbonate ta hanyar gudanar da gwaje-gwajen ramin iska a kan tuddan yashi don tantance girman zaizayar iska, saurin karyewar iyaka da juriyar jefa yashi a cikin iska, da kuma ma'aunin penetrometer da nazarin ƙananan abubuwa (misali nazarin X-ray diffraction (XRD) da kuma duba na'urar daukar hoto ta electron microscopy (SEM)).
Samar da sinadarin calcium carbonate yana buƙatar ions na calcium da ions na carbonate. Ana iya samun ions na calcium daga tushen calcium daban-daban kamar calcium chloride, calcium hydroxide, da foda madara mai laushi54,55. Ana iya samar da ions na carbonate ta hanyoyi daban-daban na microbial kamar urea hydrolysis da aerobic ko anaerobic oxidation na organic matter56. A cikin wannan binciken, an samo ions na carbonate daga amsawar oxidation na formate da acetate. Bugu da ƙari, mun yi amfani da gishirin calcium na formate da acetate don samar da tsantsar calcium carbonate, don haka aka sami CO2 da H2O kawai a matsayin samfuran da suka rage. A cikin wannan tsari, abu ɗaya kawai ke aiki a matsayin tushen calcium da tushen carbonate, kuma babu ammonia da aka samar. Waɗannan halaye suna sa hanyar samar da sinadarin calcium da carbonate da muka ɗauka a matsayin abin alfahari.
An nuna halayen da suka dace na calcium formate da calcium acetate don samar da calcium carbonate a cikin dabara (7)-(14). Dabaru (7)-(11) sun nuna cewa calcium formate yana narkewa a cikin ruwa don samar da formic acid ko tsari. Saboda haka maganin shine tushen ions na calcium da hydroxide kyauta (dabaru 8 da 9). Sakamakon oxidation na formic acid, ana canza ƙwayoyin carbon a cikin formic acid zuwa carbon dioxide (dabaru 10). A ƙarshe an samar da calcium carbonate (dabaru 11 da 12).
Hakazalika, ana samun sinadarin calcium carbonate daga sinadarin calcium acetate (daidaitawa 13-15), sai dai acetic acid ko acetate an samar da shi maimakon formic acid.
Ba tare da kasancewar enzymes ba, ba za a iya haɗa acetate da formate a zafin ɗaki ba. FDH (formate dehydrogenase) da CoA (coenzyme A) suna haɓaka oxidation na formate da acetate don samar da carbon dioxide, bi da bi (Eqs. 16, 17) 57, 58, 59. Kwayoyin cuta daban-daban suna iya samar da waɗannan enzymes, kuma ƙwayoyin cuta heterotrophic, wato Bacillus subtilis (PTCC #1204 (Persian Type Culture Collection), wanda kuma aka sani da NCIMB #13061 (International Collection of Bacteria, Yeast, Phage, Plasmids, Shuka Tsaba da Shuke-shuken Kwayoyin Halitta)) da Bacillus amyloliquefaciens (PTCC #1732, NCIMB #12077), an yi amfani da su a cikin wannan binciken. An noma waɗannan ƙwayoyin cuta a cikin wani abu mai ɗauke da peptone nama (5 g/L) da kuma ruwan nama (3 g/L), wanda ake kira broth nutrient (NBR) (105443 Merck).
Saboda haka, an shirya wasu nau'ikan sinadarai guda huɗu don haifar da ruwan sama na calcium carbonate ta amfani da tushen calcium guda biyu da ƙwayoyin cuta guda biyu: calcium formate da Bacillus subtilis (FS), calcium formate da Bacillus amyloliquefaciens (FA), calcium acetate da Bacillus subtilis (AS), da calcium acetate da Bacillus amyloliquefaciens (AA).
A kashi na farko na ƙirar gwaji, an gudanar da gwaje-gwaje don tantance mafi kyawun haɗin da zai cimma matsakaicin samar da sinadarin calcium carbonate. Tunda samfuran ƙasa sun ƙunshi sinadarin calcium carbonate, an tsara jerin gwaje-gwajen gwaji na farko don auna CaCO3 daidai da haɗuwa daban-daban, kuma an kimanta gaurayen maganin al'adu da maganin tushen calcium. Ga kowane haɗin maganin tushen calcium da ƙwayoyin cuta da aka bayyana a sama (FS, FA, AS, da AA), abubuwan ingantawa (yawan sinadarin calcium, lokacin warkarwa, yawan sinadarin bacteria da aka auna ta hanyar yawan haske na maganin (OD), rabon maganin calcium zuwa ƙwayoyin cuta, da pH) an kuma yi amfani da su a gwaje-gwajen ramin iska na maganin yashi da aka bayyana a cikin sassan da ke gaba.
Ga kowane haɗuwa, an gudanar da gwaje-gwaje 150 don nazarin tasirin ruwan sama na CaCO3 da kuma kimanta abubuwa daban-daban, wato yawan sinadarin calcium, lokacin warkarwa, ƙimar OD na ƙwayoyin cuta, rabon maganin ƙwayoyin cuta zuwa ga sinadarin calcium da kuma pH yayin iskar oxygen aerobic na kwayoyin halitta (Tebur 1). An zaɓi kewayon pH don ingantaccen tsari bisa lanƙwasa girma na Bacillus subtilis da Bacillus amyloliquefaciens don samun saurin girma. An yi bayani dalla-dalla game da wannan a cikin sashin Sakamako.
An yi amfani da matakai masu zuwa don shirya samfuran don matakin ingantawa. An fara shirya maganin MICP ta hanyar daidaita pH na farko na yanayin al'ada sannan aka rufe shi da kansa a 121 °C na minti 15. Daga nan aka yi wa nau'in allurar allurar a cikin iska mai laminar kuma aka ajiye shi a cikin injin girgiza a 30 °C da 180 rpm. Da zarar OD na ƙwayoyin cuta ya kai matakin da ake so, an haɗa shi da maganin tushen calcium a cikin rabon da ake so (Hoto na 1a). An bar maganin MICP ya amsa ya kuma ƙarfafa a cikin injin girgiza a 220 rpm da 30 °C na ɗan lokaci wanda ya kai ƙimar da aka nufa. An raba CaCO3 da aka haƙa bayan an yi shi a 6000 g na minti 5 sannan aka bushe a 40 °C don shirya samfuran don gwajin calcimeter (Hoto na 1b). An auna ruwan sama na CaCO3 ta amfani da na'urar auna sinadari ta Bernard, inda foda na CaCO3 ke amsawa da 1.0 N HCl (ASTM-D4373-02) don samar da CO2, kuma girman wannan iskar gas shine ma'aunin abun cikin CaCO3 (Hoto na 1c). Don canza girman CO2 zuwa abun cikin CaCO3, an samar da lanƙwasa ta daidaitawa ta hanyar wanke foda na CaCO3 mai tsarki tare da 1 N HCl da kuma tsara shi akan CO2 da aka haɓaka. An binciki yanayin da tsarkin foda na CaCO3 da aka haƙa ta amfani da hoton SEM da nazarin XRD. An yi amfani da na'urar hangen nesa mai girman 1000 don nazarin samuwar calcium carbonate a kusa da ƙwayoyin cuta, matakin calcium carbonate da aka samar, da kuma aikin ƙwayoyin cuta.
Tafkin Dejegh sanannen yanki ne da ya lalace sosai a kudu maso yammacin lardin Fars na Iran, kuma masu binciken sun tattara samfuran ƙasa da iska ta lalata daga yankin. An ɗauki samfuran daga saman ƙasa don binciken. Gwaje-gwajen alamu akan samfuran ƙasa sun nuna cewa ƙasar ba ta da kyau a tsaftace ta da ƙasa mai yashi kuma an rarraba ta a matsayin SP-SM bisa ga Tsarin Rarraba Ƙasa Mai Haɗaka (USC) (Hoto na 2a). Binciken XRD ya nuna cewa ƙasar Dejegh galibi ta ƙunshi calcite da quartz (Hoto na 2b). Bugu da ƙari, nazarin EDX ya nuna cewa wasu abubuwa kamar Al, K, da Fe suma suna nan a ƙananan rabo.
Domin shirya ramukan dakin gwaje-gwaje don gwajin zaizayar ƙasa, an niƙa ƙasa daga tsayin mm 170 ta hanyar rami mai diamita 10 mm zuwa wani wuri mai tauri, wanda ya haifar da tsayin mm 60 da diamita 210 mm. A yanayi, ƙananan ramukan yashi masu yawa ana samar da su ta hanyar hanyoyin aeolian. Hakazalika, samfurin da aka shirya ta amfani da hanyar da ke sama yana da mafi ƙarancin yawa, γ = 14.14 kN/m³, yana samar da mazubin yashi da aka ajiye a saman kwance tare da kusurwar hutawa kusan 29.7°.
Mafi kyawun maganin MICP da aka samu a sashin da ya gabata an fesa shi a kan gangaren dune a ƙimar amfani da 1, 2 da 3 lm-2 sannan aka adana samfuran a cikin incubator a zafin 30 °C (Hoto na 3) na tsawon kwanaki 9 (watau lokacin warkarwa mafi kyau) sannan aka fitar da su don gwajin ramin iska.
Ga kowace magani, an shirya samfura huɗu, ɗaya don auna abun ciki na calcium carbonate da ƙarfin saman ta amfani da penetrometer, sannan sauran samfura uku an yi amfani da su don gwaje-gwajen zaizayar ƙasa a gudu uku daban-daban. A cikin gwaje-gwajen ramin iska, an ƙayyade adadin zaizayar ƙasa a saurin iska daban-daban, sannan an ƙayyade saurin karyewar iyaka ga kowane samfurin magani ta amfani da taswirar adadin zaizayar ƙasa da saurin iska. Baya ga gwaje-gwajen zaizayar ƙasa, an yi wa samfuran da aka yi wa magani bam ɗin yashi (watau gwaje-gwajen tsalle). An shirya ƙarin samfura biyu don wannan dalili a ƙimar aikace-aikacen L 2 da 3 m−2. Gwajin yashi ya ɗauki mintuna 15 tare da kwararar 120 gm−1, wanda ke cikin kewayon ƙimar da aka zaɓa a cikin binciken da ya gabata60,61,62. Nisa tsakanin bututun ƙarfe da tushen dune shine 800 mm, wanda ke da mm 100 sama da ƙasan ramin. An saita wannan matsayi ta yadda kusan dukkan ƙwayoyin yashi masu tsalle suka faɗi akan dune.
An gudanar da gwajin ramin iska a cikin ramin iska mai buɗewa mai tsawon mita 8, faɗin mita 0.4 da tsayi mita 1 (Hoto na 4a). An yi ramin iskar ne da zanen ƙarfe mai galvanized kuma yana iya samar da saurin iska har zuwa mita 25/s. Bugu da ƙari, ana amfani da na'urar canza mita don daidaita mitar fanka da kuma ƙara mita a hankali don samun saurin iskar da aka nufa. Hoto na 4b yana nuna zane-zanen tuddan yashi da iska ta lalata da kuma yanayin saurin iska da aka auna a cikin ramin iska.
A ƙarshe, don kwatanta sakamakon tsarin MICP mara urealytic da aka gabatar a cikin wannan binciken da sakamakon gwajin sarrafa urealytic MICP, an kuma shirya samfuran dune kuma an yi musu magani da maganin halittu wanda ya ƙunshi urea, calcium chloride da Sporosarcina pasteurii (tunda Sporosarcina pasteurii yana da babban ikon samar da urease63). Yawan gani na maganin ƙwayoyin cuta shine 1.5, kuma yawan urea da calcium chloride sune 1 M (an zaɓa bisa ga ƙimar da aka ba da shawarar a cikin binciken da ya gabata36,64,65). Maganin al'ada ya ƙunshi ruwan sinadari (8 g/L) da urea (20 g/L). An fesa maganin ƙwayoyin cuta a saman dune kuma an bar shi na tsawon awanni 24 don haɗawa da ƙwayoyin cuta. Bayan awanni 24 na haɗawa, an fesa maganin siminti (calcium chloride da urea). Daga nan za a kira gwajin sarrafa urealytic MICP UMC. An samo sinadarin calcium carbonate na samfuran ƙasa da aka yi wa magani ta hanyar urealytic da kuma waɗanda ba a yi wa magani ta hanyar urealytic ba ta hanyar wankewa bisa ga tsarin da Choi et al.66 suka gabatar.
Siffa ta 5 ta nuna lanƙwasa girma na Bacillus amyloliquefaciens da Bacillus subtilis a cikin yanayin al'ada (maganin gina jiki) tare da matsakaicin pH na farko na 5 zuwa 10. Kamar yadda aka nuna a cikin hoton, Bacillus amyloliquefaciens da Bacillus subtilis sun girma da sauri a pH 6-8 da 7-9, bi da bi. Saboda haka, an ɗauki wannan kewayon pH a matakin ingantawa.
Lanƙwasa girma na (a) Bacillus amyloliquefaciens da (b) Bacillus subtilis a ƙimar pH daban-daban na matsakaicin sinadarin gina jiki.
Siffa ta 6 ta nuna adadin carbon dioxide da aka samar a cikin Bernard limemeter, wanda ke wakiltar sinadarin calcium carbonate da aka haƙa (CaCO3). Tunda an daidaita abu ɗaya a cikin kowane haɗuwa kuma an bambanta sauran abubuwan, kowane maki akan waɗannan zane-zanen ya yi daidai da matsakaicin adadin carbon dioxide a cikin wannan saitin gwaje-gwajen. Kamar yadda aka nuna a cikin sigar, yayin da yawan sinadarin calcium ya ƙaru, samar da sinadarin calcium carbonate ya ƙaru. Saboda haka, yawan sinadarin calcium yana shafar samar da sinadarin calcium carbonate kai tsaye. Tunda tushen sinadarin calcium da tushen carbon iri ɗaya ne (watau, sinadarin calcium formate da sinadarin calcium acetate), yawan sinadarin calcium ions da aka saki, yawan sinadarin calcium carbonate da aka samar (Hoto na 6a). A cikin tsarin AS da AA, samar da sinadarin calcium carbonate ya ci gaba da ƙaruwa tare da ƙaruwar lokacin warkarwa har sai adadin sinadarin ya kusan canzawa bayan kwana 9. A cikin tsarin FA, ƙimar samuwar sinadarin calcium carbonate ta ragu lokacin da lokacin warkarwa ya wuce kwana 6. Idan aka kwatanta da sauran tsarin, tsarin FS ya nuna ƙarancin adadin sinadarin calcium carbonate bayan kwana 3 (Hoto na 6b). A cikin tsarin FA da FS, an samu kashi 70% da 87% na jimillar samar da sinadarin calcium carbonate bayan kwana uku, yayin da a cikin tsarin AA da AS, wannan kaso ya kasance kusan kashi 46% da 45% ne kawai, bi da bi. Wannan yana nuna cewa tsarin formic acid yana da mafi girman matakin samuwar CaCO3 a matakin farko idan aka kwatanta da tsarin acetate. Duk da haka, saurin samuwar yana raguwa tare da ƙaruwar lokacin warkarwa. Za a iya kammalawa daga Hoto na 6c cewa ko da a yawan ƙwayoyin cuta sama da OD1, babu wani muhimmin gudummawa ga samuwar sinadarin calcium carbonate.
Canji a cikin girman CO2 (da kuma abun da ke cikin CaCO3 mai dacewa) wanda aka auna ta hanyar Bernard calcimeter a matsayin aikin (a) yawan sinadarin calcium, (b) lokacin saitawa, (c) OD, (d) pH na farko, (e) rabon sinadarin calcium zuwa maganin ƙwayoyin cuta (ga kowane tsari); da kuma (f) matsakaicin adadin sinadarin calcium carbonate da aka samar ga kowane haɗin tushen calcium da ƙwayoyin cuta.
Dangane da tasirin pH na farko na matsakaici, Hoto na 6d ya nuna cewa ga FA da FS, samar da CaCO3 ya kai matsakaicin ƙima a pH 7. Wannan lura ya yi daidai da binciken da aka yi a baya cewa enzymes na FDH sun fi karko a pH 7-6.7. Duk da haka, ga AA da AS, ruwan sama na CaCO3 ya ƙaru lokacin da pH ya wuce 7. Nazarin da aka yi a baya ya kuma nuna cewa mafi kyawun kewayon pH don aikin enzyme na CoA shine daga 8 zuwa 9.2-6.8. Idan aka yi la'akari da cewa mafi kyawun kewayon pH don aikin enzyme na CoA da haɓakar B. amyloliquefaciens sune (8-9.2) da (6-8), bi da bi (Hoto na 5a), ana sa ran mafi kyawun pH na tsarin AA zai zama 8, kuma nau'ikan pH guda biyu sun haɗu. An tabbatar da wannan gaskiyar ta hanyar gwaje-gwaje, kamar yadda aka nuna a Hoto na 6d. Tunda mafi kyawun pH don girman B. subtilis shine 7-9 (Hoto na 5b) kuma mafi kyawun pH don aikin enzyme na CoA shine 8-9.2, ana sa ran matsakaicin yawan ruwan sama na CaCO3 zai kasance a cikin kewayon pH na 8-9, wanda aka tabbatar ta hanyar Hoto na 6d (watau, mafi kyawun pH na ruwan sama shine 9). Sakamakon da aka nuna a Hoto na 6e ya nuna cewa mafi kyawun rabo na mafi kyawun maganin tushen calcium zuwa maganin ƙwayoyin cuta shine 1 don duka maganin acetate da formate. Don kwatantawa, an kimanta aikin tsari daban-daban (watau, AA, AS, FA, da FS) bisa ga matsakaicin samar da CaCO3 a ƙarƙashin yanayi daban-daban (watau, yawan tushen calcium, lokacin warkarwa, OD, rabon tushen calcium zuwa maganin ƙwayoyin cuta, da kuma pH na farko). Daga cikin dabarun da aka yi nazari a kansu, tsarin FS yana da mafi girman samar da CaCO3, wanda ya ninka sau uku na tsarin AA (Hoto na 6f). An gudanar da gwaje-gwaje huɗu na sarrafawa marasa ƙwayoyin cuta don duka tushen calcium kuma ba a lura da ruwan sama na CaCO3 ba bayan kwanaki 30.
Hotunan na'urar hangen nesa ta dukkan hanyoyin sun nuna cewa vaterite shine babban matakin da aka samar da sinadarin calcium carbonate (Hoto na 7). Lu'ulu'u na vaterite suna da siffar zagaye69,70,71. An gano cewa sinadarin calcium carbonate ya zube a kan ƙwayoyin cuta saboda saman ƙwayoyin cuta yana da caji mara kyau kuma yana iya aiki azaman mai shaye-shaye ga cations na divalent. Idan aka ɗauki samfurin FS a matsayin misali a cikin wannan binciken, bayan awanni 24, sinadarin calcium carbonate ya fara samuwa a kan wasu ƙwayoyin cuta (Hoto na 7a), kuma bayan awanni 48, adadin ƙwayoyin cuta da aka lulluɓe da sinadarin calcium carbonate ya ƙaru sosai. Bugu da ƙari, kamar yadda aka nuna a Hoto na 7b, ana iya gano ƙwayoyin vaterite. A ƙarshe, bayan awanni 72, da alama adadin ƙwayoyin cuta suna ɗaure da lu'ulu'u na vaterite, kuma adadin ƙwayoyin vaterite ya ƙaru sosai (Hoto na 7c).
An lura da hazo na CaCO3 a cikin abubuwan da aka haɗa na FS a tsawon lokaci: (a) 24, (b) 48 da (c) awanni 72.
Domin ƙarin bincike kan yanayin yanayin da aka yi amfani da shi, an yi nazarin diffraction na X-ray (XRD) da SEM na foda. An yi nazarin XRD spectra (Hoto na 8a) da SEM micrographs (Hoto na 8b, c) sun tabbatar da kasancewar lu'ulu'u na vaterite, domin suna da siffar latas kuma an lura da daidaito tsakanin kololuwar vaterite da kololuwar precipitate.
(a) Kwatanta spectra na X-ray diffraction na CaCO3 da vaterite da aka samar. Micrographs na SEM na vaterite a (b) 1 kHz da (c) 5.27 kHz girma, bi da bi.
An nuna sakamakon gwaje-gwajen ramin iska a Hoto na 9a, b. Ana iya gani daga Hoto na 9a cewa saurin zaizayar ƙasa (TDV) na yashi da ba a yi masa magani ya kai kimanin m4.32/s. A ƙimar aikace-aikacen 1 l/m² (Hoto na 9a), gangaren layukan asarar ƙasa don ɓangarorin FA, FS, AA da UMC kusan iri ɗaya ne da na dune da ba a yi masa magani ba. Wannan yana nuna cewa maganin da aka yi a wannan ƙimar aikace-aikacen ba shi da tasiri kuma da zarar saurin iska ya wuce TDV, ɓawon ƙasa mai siriri ya ɓace kuma ƙimar zaizayar ƙasa iri ɗaya ne da na dune da ba a yi masa magani ba. Zurfin zaizayar ƙasa na ɓangaren AS shima ya yi ƙasa da na sauran ɓangarorin da ke da ƙananan abscissas (watau TDV) (Hoto na 9a). Kibiyoyi a Hoto na 9b suna nuna cewa a matsakaicin saurin iska na m25/s, babu wani zaizayar ƙasa da ya faru a cikin dunes da aka yi wa magani a ƙimar aikace-aikacen 2 da 3 l/m². A wata ma'anar, ga FS, FA, AS da UMC, dunes sun fi jure wa zaizayar iska da CaCO³ ya haifar a yawan amfani da shi na 2 da 3 l/m² fiye da matsakaicin saurin iska (watau 25 m/s). Don haka, ƙimar TDV na 25 m/s da aka samu a cikin waɗannan gwaje-gwaje shine ƙananan iyaka ga ƙimar aikace-aikacen da aka nuna a Hoto na 9b, sai dai idan yanayin AA ne, inda TDV kusan daidai yake da matsakaicin saurin ramin iska.
Gwajin zaizayar iska (a) Rage nauyi idan aka kwatanta da saurin iska (ƙimar amfani 1 l/m2), (b) Saurin yagewa idan aka kwatanta da saurin amfani da tsari (CA don calcium acetate, CF don calcium formate).
Siffa ta 10 ta nuna yadda saman tuddan yashi da aka yi wa magani da tsari daban-daban da kuma yawan amfani bayan gwajin jefa yashi, kuma an nuna sakamakon adadi a Siffa ta 11. Ba a nuna yanayin da ba a yi wa magani ba saboda bai nuna juriya ba kuma ya lalace gaba ɗaya (jimillar asarar nauyi) a lokacin gwajin jefa yashi. A bayyane yake daga Siffa ta 11 cewa samfurin da aka yi wa magani da biocomposition AA ya rasa kashi 83.5% na nauyinsa a lokacin amfani da shi na 2 l/m2, yayin da sauran samfuran suka nuna ƙasa da kashi 30% na zaizayar ƙasa a lokacin aikin jefa yashi. Lokacin da aka ƙara yawan amfani da shi zuwa 3 l/m2, duk samfuran da aka yi wa magani sun rasa ƙasa da kashi 25% na nauyinsu. A duka ƙimar amfani, FS mai hade ya nuna mafi kyawun juriya ga jefa yashi. Matsakaicin juriya da mafi ƙarancin juriya ga jefa yashi a cikin samfuran da aka yi wa magani da FS da AA za a iya danganta su da matsakaicin da mafi ƙarancin ruwan sama na CaCO3 (Siffa ta 6f).
Sakamakon jefa bom a kan tudun yashi na abubuwa daban-daban a cikin ƙimar kwararar ruwa na 2 da 3 l/m2 (kibiyoyi suna nuna alkiblar iska, giciye suna nuna alkiblar iska a tsaye zuwa saman zane).
Kamar yadda aka nuna a Hoto na 12, yawan sinadarin calcium carbonate na dukkan dabarar ya ƙaru yayin da yawan amfani ya ƙaru daga 1 L/m² zuwa 3 L/m². Bugu da ƙari, a duk yawan amfani, dabarar da ke da mafi girman sinadarin calcium carbonate ita ce FS, sai kuma FA da UMC. Wannan yana nuna cewa waɗannan dabarar na iya samun juriya mafi girma a saman.
Siffa ta 13a ta nuna canjin juriyar saman samfuran ƙasa marasa magani, sarrafawa da kuma waɗanda aka yi wa magani ta hanyar gwajin permeameter. Daga wannan siffa, a bayyane yake cewa juriyar saman samfuran UMC, AS, FA da FS ta ƙaru sosai tare da ƙaruwar yawan amfani. Duk da haka, ƙaruwar ƙarfin saman bai yi yawa ba a cikin tsarin AA. Kamar yadda aka nuna a cikin siffa, tsarin FA da FS na MICP mara urea yana da mafi kyawun damar shiga saman idan aka kwatanta da MICP mai urea. Siffa ta 13b ta nuna canjin TDV tare da juriyar saman ƙasa. Daga wannan siffa, a bayyane yake cewa ga dunes masu juriyar saman sama fiye da 100 kPa, saurin cire iyakar zai wuce m25/s. Tunda juriyar saman a wuri ana iya auna ta cikin sauƙi ta hanyar permeameter, wannan ilimin zai iya taimakawa wajen kimanta TDV idan babu gwajin ramin iska, don haka yana aiki a matsayin alamar kula da inganci don aikace-aikacen filin.
An nuna sakamakon SEM a Hoto na 14. Hotuna na 14a-b sun nuna ƙananan barbashi na samfurin ƙasa mara magani, wanda a bayyane yake nuna cewa yana da haɗin kai kuma ba shi da haɗin kai na halitta ko siminti. Hoto na 14c yana nuna ƙaramin SEM na samfurin sarrafawa da aka yi wa magani da MICP mai lalacewa ta urea. Wannan hoton yana nuna kasancewar abubuwan da suka haifar da CaCO3 a matsayin polymorphs na calcite. Kamar yadda aka nuna a Hoto na 14d-o, CaCO3 mai fashewa yana haɗa barbashi tare; ana iya gano lu'ulu'u masu siffar vertical vaterite a cikin ƙananan hotunan SEM. Sakamakon wannan binciken da binciken da ya gabata sun nuna cewa haɗin CaCO3 da aka samar a matsayin ƙwayoyin vaterite suma na iya samar da ƙarfin injiniya mai ma'ana; sakamakonmu ya nuna cewa juriyar saman yana ƙaruwa zuwa 350 kPa kuma saurin rabuwar iyaka yana ƙaruwa daga 4.32 zuwa fiye da 25 m/s. Wannan sakamakon ya yi daidai da sakamakon binciken da aka yi a baya cewa matrix na CaCO3 da aka yi wa MICP-precipitated shine vaterite, wanda ke da ƙarfin injina mai ma'ana da juriya ga zaizayar iska13,40 kuma yana iya kiyaye juriya ga zaizayar iska mai ma'ana koda bayan kwanaki 180 na fallasa ga yanayin muhalli na fili13.
(a, b) Ma'aunin SEM na ƙasa mara magani, (c) Kula da lalata urea na MICP, (df) Samfuran da aka yi wa magani da AA, (gi) Samfuran da aka yi wa magani da AS, (jl) Samfuran da aka yi wa magani da FA, da (mo) Samfuran da aka yi wa magani da FS a ƙimar amfani da 3 L/m2 a girma daban-daban.
Siffa ta 14d-f ta nuna cewa bayan an yi amfani da sinadaran AA, an samu sinadarin calcium carbonate a saman da kuma tsakanin ƙwayoyin yashi, yayin da aka kuma lura da wasu ƙwayoyin yashi marasa rufi. Ga abubuwan da ke cikin AS, kodayake adadin CaCO3 da aka samar bai ƙaru sosai ba (Hoto na 6f), adadin hulɗa tsakanin ƙwayoyin yashi da CaCO3 ya haifar ya ƙaru sosai idan aka kwatanta da ƙwayoyin AA (Hoto na 14g-i).
Daga Hotuna 14j-l da 14m-o, a bayyane yake cewa amfani da sinadarin calcium a matsayin tushen calcium yana haifar da ƙarin ƙaruwa a cikin ruwan sama na CaCO3 idan aka kwatanta da mahaɗin AS, wanda ya yi daidai da ma'aunin ma'aunin calcium a Hoto na 6f. Wannan ƙarin CaCO3 ya bayyana a matsayin wanda aka ajiye galibi akan ƙwayoyin yashi kuma ba lallai bane ya inganta ingancin hulɗar ba. Wannan yana tabbatar da halayen da aka lura a baya: duk da bambance-bambancen da ke cikin adadin ruwan sama na CaCO3 (Hoto na 6f), tsari uku (AS, FA da FS) ba su bambanta sosai ba dangane da aikin anti-eolian (iska) (Hoto na 11) da juriyar saman (Hoto na 13a).
Domin a iya ganin ƙwayoyin cuta masu rufi da CaCO3 da kuma tasirin ƙwayoyin cuta a kan lu'ulu'u masu fashewa, an ɗauki ƙananan hotuna na SEM masu girma kuma an nuna sakamakon a Hoto na 15. Kamar yadda aka nuna, calcium carbonate yana taruwa akan ƙwayoyin cuta kuma yana samar da ƙwayoyin da ake buƙata don ruwan sama a can. Hoton kuma yana nuna haɗin gwiwa masu aiki da marasa aiki da CaCO3 ya haifar. Ana iya kammalawa cewa duk wani ƙaruwa a cikin haɗin gwiwa marasa aiki ba lallai bane ya haifar da ƙarin ci gaba a cikin halayen injiniya. Saboda haka, ƙaruwar ruwan sama na CaCO3 ba lallai bane ya haifar da ƙarin ƙarfi na injiniya kuma tsarin ruwan sama yana taka muhimmiyar rawa. An kuma yi nazarin wannan batu a cikin ayyukan Terzis da Laloui72 da Soghi da Al-Kabani45,73. Don ƙarin bincika alaƙar da ke tsakanin tsarin ruwan sama da ƙarfin injina, ana ba da shawarar nazarin MICP ta amfani da hoton µCT, wanda ya wuce iyakokin wannan binciken (watau, gabatar da haɗuwa daban-daban na tushen calcium da ƙwayoyin cuta don MICP mara ammonia).
CaCO3 ya haifar da haɗin gwiwa mai aiki da mara aiki a cikin samfuran da aka yi wa magani da (a) abun da ke cikin AS da (b) abun da ke cikin FS kuma ya bar alamar ƙwayoyin cuta a kan laka.
Kamar yadda aka nuna a cikin Hotuna 14j-o da 15b, akwai fim ɗin CaCO (bisa ga binciken EDX, kashi na kowanne abu a cikin fim ɗin shine carbon 11%, oxygen 46.62% da calcium 42.39%, wanda yake kusa da kashi na CaCO2 a cikin Hoto na 16). Wannan fim ɗin ya ƙunshi lu'ulu'u na vaterite da barbashi na ƙasa, wanda ke taimakawa wajen kiyaye amincin tsarin ƙasa-laka. An lura da kasancewar wannan fim ɗin ne kawai a cikin samfuran da aka yi wa magani da tsarin da aka yi amfani da shi bisa ga tsari.
Tebur na 2 ya kwatanta ƙarfin saman ƙasa, saurin cire iyaka, da kuma yawan CaCO3 da ke cikin ƙasa da aka yi wa magani da hanyoyin MICP masu lalata urea da waɗanda ba su lalata urea a cikin binciken da aka yi a baya da kuma wannan binciken. Nazarin kan juriyar zaizayar iska na samfuran dune da aka yi wa magani da MICP ba su da iyaka. Meng da abokan aikinsa sun binciki juriyar zaizayar iska na samfuran dune masu lalata urea da aka yi wa magani da MICP ta amfani da na'urar hura ganye,13 yayin da a cikin wannan binciken, an gwada samfuran dune marasa lalata urea (da kuma hanyoyin sarrafa rage urea) a cikin ramin iska kuma an yi musu magani da haɗuwar ƙwayoyin cuta da abubuwa guda huɗu daban-daban.
Kamar yadda ake gani, wasu binciken da aka yi a baya sun yi la'akari da yawan amfani da ya wuce 4 L/m213,41,74. Ya kamata a lura cewa yawan amfani da shi ba zai yiwu ya zama mai sauƙin amfani a fagen daga mahangar tattalin arziki ba saboda farashin da ke tattare da samar da ruwa, jigilar kaya da kuma amfani da ruwa mai yawa. Ƙananan ƙimar amfani kamar 1.62-2 L/m2 suma sun sami ƙarfin saman da ya kai 190 kPa da TDV fiye da 25 m/s. A cikin wannan binciken, dunes da aka yi wa magani da MICP mai tushen tsari ba tare da lalacewar urea ba sun sami ƙarfin saman da ya yi daidai da waɗanda aka samu tare da hanyar lalata urea a cikin adadin aikace-aikacen iri ɗaya (watau, samfuran da aka yi wa magani da MICP mai tushen tsari ba tare da lalacewar urea ba suma sun sami damar cimma irin wannan kewayon ƙimar ƙarfin saman kamar yadda Meng et al., 13, Hoto na 13a) ya ruwaito a mafi girman ƙimar aikace-aikacen. Haka kuma za a iya ganin cewa a yawan amfani da sinadarin calcium carbonate don rage zaizayar iska a saurin iska na 25 m/s ya kai 2.25% ga MICP mai tushen tsari ba tare da lalata urea ba, wanda yake kusa da adadin da ake buƙata na CaCO3 (watau 2.41%) idan aka kwatanta da dunes da aka yi wa magani da MICP mai sarrafawa tare da lalata urea a daidai lokacin amfani da kuma saurin iska iri ɗaya (25 m/s).
Saboda haka, za a iya kammalawa daga wannan tebur cewa hanyar lalata urea da hanyar lalata ba tare da urea ba na iya samar da aiki mai kyau dangane da juriyar saman da TDV. Babban bambanci shine hanyar lalata ba tare da urea ba ba ta ƙunshi ammonia ba saboda haka tana da ƙarancin tasirin muhalli. Bugu da ƙari, hanyar MICP mai tushen tsari ba tare da lalata urea da aka gabatar a cikin wannan binciken da alama tana aiki mafi kyau fiye da hanyar MICP mai tushen acetate ba tare da lalata urea ba. Kodayake Mohebbi et al. sun yi nazarin hanyar MICP mai tushen acetate ba tare da lalata urea ba, bincikensu ya haɗa da samfura akan saman lebur9. Saboda matakin yaɗuwar da ya haifar da samuwar eddy a kusa da samfuran dune da kuma yankewar da aka samu, wanda ke haifar da ƙarancin TDV, ana sa ran zaizayar iska ta samfuran dune zai fi bayyana fiye da na saman lebur a daidai wannan gudu.