Management of hydrogen sulphide generation at a Kraft paper mill

dc.contributor.advisorLeske, Anthonyen
dc.contributor.advisorSchoeman, J.J. (Jakob Johannes)en
dc.contributor.emailemrava@buckman.comen
dc.contributor.postgraduateRava, Eleonora Maria Elizabeth
dc.date.accessioned2013-09-07T12:39:05Z
dc.date.available2008-09-22en
dc.date.available2013-09-07T12:39:05Z
dc.date.created2008-04-11en
dc.date.issued2008-09-22en
dc.date.submitted2008-09-15en
dc.descriptionDissertation (MSc(Applied Science))--University of Pretoria, 2008.en
dc.description.abstractA local integrated pulp and paper Kraft mill had come under pressure from the local communities and mill personnel to reduce the odours that were perceived to be generated at the Farm Dams and irrigation farm situated adjacent to the mill. The typical odours associated with Kraft mills are due to the generation of four reduced sulphur compounds such as hydrogen sulphide (H2S), methyl-mercaptan (CH3SH), dimethyl-sulphide (CH3)2S and dimethyl-disulphide (CH3)2S2. These compounds are collectively referred to as Total Reduced Sulphur (TRS) components which are generated as a direct result of the Kraft pulping and chemical recovery process. These components can either be in the gaseous or aqueous phase depending on the characteristics of the effluent. Gaseous and aqueous TRS profiling of the mill indicated that hydrogen sulphide (H2S) was the main odour component generated and emitted from the Clarifiers and the Treated Effluent Transfer Sump (TETS) at the effluent treatment plant. The hydrogen sulphide (H2S) emission levels were affected by process upsets, sludge removal frequencies, chemical composition of the effluent, Sulphate Reducing Bacteria (SRB) activity, pH and temperature fluctuations. Treatment options such as pH control using slaked lime, dosing of biocides, addition of biomodifiers and/or a sulphate reduction inhibitor were investigated. The use of slaked lime, Ca(OH) 2, for pH control was not practical due to continuous pH fluctuations, increasing the pH would increase the scaling tendencies of the effluent and would also affect the soil cation-anion exchange properties of the irrigated farm land. The use of non-oxidising biocides was effective in reducing SRB activity between 99.2% and 99.8% at dosages between 4 mg/l and 25 mg/l. However, the use of biocides was not considered as a long term treatment option due to the various disadvantages such as the stability of the biocides at fluctuating pH and temperatures, half-life, environmental accumulation, toxicity and costs. The aqueous H2S level was reduced by 79% using different combinations of biomodifiers (nitrates, nitrites, molybdenum). Increasing the dosages of the biomodifiers (> 500mg/l) would be required to increase the reduction of H2S levels by more than 79%. The increased dosages would significantly increase the cost of the treatment programme. The accumulation of nitrates, nitrites and molybdenum could affect the soil texture, cation-anion exchange capacity, permeability, Sodium Absorption Ratio (SAR) and nutrient availability. A more environmentally friendly and cost effective treatment was found using sodium nitrate (biomodifier) together with AQ (sulphate reduction inhibitor). The continuous dosing of 50 mg/l sodium nitrate together with 4 mg/l AQ would be effective in reducing the average aqueous H2S levels (40 mg/l) by at least 92%. This treatment would also be compatible with aeration or oxidation procedures to further increase the removal of H2S to achieve an aqueous H2S level of <1 mg/l. Aeration or oxidation would also increase the dissolved oxygen and COD levels, increase the inhibition of SRB activity and oxidise any reduced sulphur. The dosing of sodium nitrate and AQ to control the generation of H2S is not patented in South Africa. It can, therefore, be used to treat the Kraft mill effluent without violating any intellectual property rights in South Africa.en
dc.description.availabilityunrestricteden
dc.description.departmentChemical Engineeringen
dc.identifier.citationa 2008en
dc.identifier.otherE1071/gmen
dc.identifier.upetdurlhttp://upetd.up.ac.za/thesis/available/etd-09152008-113200/en
dc.identifier.urihttp://hdl.handle.net/2263/27949
dc.language.isoen
dc.publisherUniversity of Pretoriaen_ZA
dc.rights© University of Pretoria 2008 E1071/en
dc.subjectSlaked limeen
dc.subjectSulphate reducing bacteriaen
dc.subjectEffluent treatment planten
dc.subjectBiomodifiersen
dc.subjectAnthraquinoneen
dc.subjectBiocidesen
dc.subjectPh controlen
dc.subjectHydrogen sulphideen
dc.subjectKraft millsen
dc.subjectOdoursen
dc.subjectSrben
dc.subjectTotal reduced sulphuren
dc.subjectTrsen
dc.subjectUCTDen_US
dc.titleManagement of hydrogen sulphide generation at a Kraft paper millen
dc.typeDissertationen

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