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Performance Evaluation of the Town of Monterery Wastewater Treatment Plant Utilizing Subsurface Flow Constructed WetlandsKiracofe, Brandon Dean 21 July 2000 (has links)
Field tests were conducted and historical operating data were evaluated to assess the performance of the Monterey WWTP utilizing subsurface flow (SF) constructed wetlands. Previous work with SF wetlands has demonstrated adequate, but variable removal of organic matter, suspended solids, and nitrogen. Few research studies have observed the generation of compounds in the wetlands that affect other treatment processes, specifically reduced compounds that contribute to the chlorine demand. This study attempts not only to distinguish the factors leading to the inadequate performance of the SF wetlands in removing organic matter and nitrogen, but also to identify the cause of the frequent occurrences of a nondetectable chlorine residual in the chlorine contact tank at the Monterey WWTP. Collection and analysis of historical operating data from January 1998 to May 2000 revealed a constantly decreasing removal of carbonaceous biochemical oxygen demand (CBOD5) by the SF wetlands and a poor removal of ammonia-N throughout the system. The decreasing removal of CBOD5 appeared to be caused by clogging of the wetland bed media by accumulated solids. The inability to remove the accumulated solids by pumping was shown. Analysis of field data also showed that the SF wetlands removed 88% of the influent TSS and 71% of the influent CBOD5, while experiencing a 18% increase in ammonia-N. Bisulfide produced in the anaerobic wetland beds accounted for 95% of the chlorine lost in contact tank. The variable production of sulfide is the cause of the frequent nondetectable chlorine concentrations observed. The results of this study suggest that chemical costs of chlorine and sulfur dioxide may be greatly reduced if bisulfide can be removed before chlorination. Also, the use of large rocks as media in SF wetland beds may significantly reduce the physical and biological removal of organic matter. / Master of Science
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Process development for co-digestion of toxic effluents : development of screening proceduresDlamini, Sithembile January 2009 (has links)
Submitted in partial fulfillment of academic requirements for the degree of Masters of Technology: Department of Chemical Engineering, Durban University of Technology, 2009. / The primary objective of this project was to establish a screening protocol which could be used
to access high strength/toxic effluent for toxicity and degradability prior to being disposed in
wastewater treatment works.
The serum bottle method (materials and method section) is simple, makes use of small glass vials
(125 mℓ-volume were used in this research) which do not require any stirring nor feeding device
or other engineered tool: a serum bottle is sealed immediately after all components are poured
inside and thereafter conducted in a batch mode and occasionally shaken to ensure adequate
homogenisation of the components. The only variables which are regularly measured are the
volume of biogas produced and gas composition. The two assays, originally developed by
Owen et al. (1979) to address the toxicity and the biodegradability have been combined in a
single test called AAT, Anaerobic Activity Test, which enables one to assess simultaneously the
inhibitory effect on the methanogenic biomass and the biodegradability of the test material as
well as the ability of the biomass to adapt to the test material and therefore to overcome the
initial inhibition.
The screening protocol is illustrated in Annexure A. The protocol consists of a sequence of
assays which employ the serum bottle methodology. A first step of the procedure is aimed at
rapidly estimating whether the effluent is potentially toxic to the methanogenic biomass and in
what concentration. The second step is a more extensive screening, aimed at precisely
characterising the toxicity of the effluent, the extent of biodegradation that can be achieved, as
well as at establishing whether a potential for adaptation of the biomass exists upon exposure. If
the sample passes the screening stage, the same serum bottle method will be used to conduct a
series of batch co-digestion experiments aimed at evaluating a convenient volumetric ratio
between the test material and the readily biodegradable substrate. Finally, a laboratory-scale codigestion
trial could simulate the full-scale process, thus enabling the selection of appropriate
operating conditions for the start-up of the full-scale implementation.
This the protocol has been used to assess the amenability to be anaerobically (co)digested of four
industrial effluents, i.e. size and distillery effluents which are classified as high strength and
scour and synthetic dye effluents classified as toxic. From the biodegradability and toxicity
assays the following conclusions were drawn. The size and distillery effluent were found to be
ii
degradable at 32 g COD/ℓ and 16 g COD /ℓ concentrations respectively. Concentrations higher
than these stipulated above were found inhibitory. Scour effluent was found to be recalcitrant at
all concentration tested and synthetic dye was 100 % degradable at 0.12 g COD/ℓ and lower and
highly inhibitory at concentration higher than 1.1 g COD/ℓ.
Co-digestion experiment using serum bottle AAT method were undertaken between effluents i.e.
size + distillery, size + scour, distillery + synthetic dye in an attempt to verify whether the
digestion performance benefits from simultaneous presence of the two substrates. The volumetric
ratios between the effluents were 1:1, 1:2, 2:1. The presence of two mixtures in the case of size
and distillery had better methane production compared to individual substrate i.e. size or
distillery separate. The mixture with volumetric flow rate ratio of 2:1 (size: distillery) was
preferable in terms of process performance as it had highest COD removal compared to the other
mixtures /ratios and individual substrates. The mixture of size and scour (2:1) had highest
degradation percentage compared to other ratios but not high enough to qualify as degradable
(less than 50 %). The mixture of distillery and synthetic dye had the same pattern with ratio of
2:1 giving the best COD conversion. The pattern than can be drawn from the degradability of
mixtures is: the degradability of mixtures increase with the increasing amount of the most
biodegradable compound/effluent in the mixture.
Serum bottle results provided the detailed information regarding the safe operating parameters
which should be used during the starting point for the larger scale investigation i.e. lab-scale
investigations. The lab scale investigations were conducted primarily to validate screening and
monitor how the digestion progresses and also to provide data for future project i.e. pilot plant
investigation. Other effluents i.e. scour and synthetic dye and their co-digestion mixture were
excluded from the lab-scale investigations since they were found to be non- biodegradable i.e.
their COD conversion was less the 50 % in the screening protocol. Due to time constrains and
other technical difficulties in the laboratory, the co-digestion of size and distillery mixture trials
we not conducted on the laboratory scale.
Laboratory-scale digestion trials showed that the best organic loading rate for distillery effluent
in terms of reactor performance and stability was 1.0g COD/ℓ with efficiency of about 45 %, and
for size was 2.0g COD/ℓ with an efficiency of 40 %. The efficiencies obtained in both effluents
trials could be greatly improved by acclimation; however these results showed that the digestion
of these effluents on the bigger scale is possible. / Water Research Commission
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PCR detection, denaturing gradient gel electrophoresis (DGGE) fingerprinting and identification of the microbial consortium in different types of UASB granulesKeyser, Maricel 12 1900 (has links)
Thesis (PhD (Food Science))--University of Stellenbosch, 2006. / High-rate anaerobic bioreactors are used for the treatment of various wastewaters, of which the upflow anaerobic sludge blanket (UASB) bioreactor has the widest application, especially in the food and beverage industries. In an UASB bioreactor sludge develops in a particular granular or flocculent form and the success of the anaerobic process relies on the formation of active and settable granules. These granules are formed by self-aggregation of bacteria that can be divided into different trophic groups that are responsible for the metabolic breakdown of organic substrates.
The successful performance of a bioreactor is influenced by the composition of the substrate which subsequently may have an impact on the microbial consortium present in the UASB granules. In order to determine if a change in the structure of the non-methanogenic microbial community takes place, UASB brewery granules were subjected to the sudden addition of different carbon sources at different concentrations. A shift in the microbial community did occur when the granules were subjected to lactate medium (5 g.l-1). No changes in the microbial community were observed when the granules were stressed with glucose medium as carbon source, regardless of an increase in the glucose concentration.
In order to better understand the effect that different wastewaters may have on the microbial consortium present in different UASB granules, the polymerase chain reaction (PCR) based denaturing gradient gel electrophoresis (DGGE) technique and sequence analysis were used to fingerprint and identify the Bacteria and Archaea present in either, winery, brewery, distillery or peach-lye canning UASB granules. Each granule type showed distinct PCR-based DGGE fingerprints with unique bands, while other bands were found to be present in all the granules regardless of the wastewater being treated. Bacillus, Pseudomonas, Bacteroides, Enterococcus, Alcaligenes, Clostridium, Shewanella, Microbacterium, Leuconostoc, Sulfurospirillum, Acidaminococcus, Vibrio, Aeromonas, Nitrospira, Synergistes, Rhodococcus, Rhodocyclus, Syntrophobacter and uncultured bacteria were identified, representing different acidogenic, acetogenic and homoacetogenic Bacteria.Different methanogenic bacteria such as Methanosaeta, Methanosarcina, Methanobacterium and uncultured bacteria belonging to the group Archaea were also fingerprinted and identified from different UASB granules. In both these studies a DGGE marker was constructed that may be used to assist in the identification of bacteria. The DGGE marker can also be used to monitor the presence of bacteria over a time period during anaerobic digestion. Bioaugmentation or the enrichment of granules results in tailor-made granules that may be used for the treatment of specific wastewaters.
One of the most important contributions to the maintenance and enhancement of UASB granule formation is the inclusion of suitable microbes in the granule structure. Enterobacter sakazakii was isolated from raw winery wastewater and was found to produce sufficient amounts of desired fatty acids. This bacteria was, therefore, incorporated into batch cultured granular sludge. In order to identify and monitor the presence of the incorporated E. sakazakii in the tailor-made granules, 16S rRNA gene sequence primers and PCR conditions were developed.
The use of molecular techniques such as PCR-based DGGE and sequence analysis proved to be successful methods to fingerprint and identify the microbial consortium present in the different UASB granules.
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Modelling biological sulphate reduction in anaerobic digestion using WEST.03 September 2010 (has links)
Researchers at Rhodes University conducted investigations into the anaerobic co-disposal of
primary sewage sludge (PSS) and high sulphate acid mine drainage (AMD) resulting in the
development of the Rhodes BioSURE Process® which forms the basis for the operation of a
pilot recycling sludge bed reactor (RSBR). Further research has been conducted by researchers
at the University of Cape Town (UCT), with the principle aim of determining the rate of
hydrolysis of PSS under rnethanogenic, acidogenic and sulphate reducing conditions in
laboratory-scale anaerobic digesters.
The University of Cape Town's Anaerobic Digestion Model No.1 (UCTADMI) which
integrates various biological anaerobic processes for the production of methane was extended
with the development of a mathematical model incorporating the processes of biosulphidogenic
reduction and the biology of sulphate reducing bacteria (SRB). Kinetic parameters used in the
model were obtained from SOtemann et al. (2005b) and Kalyuzhnyi et al. (1998).
The WEST® software was used as a platform in translation of the basic UCTADMI from
AQUASIM, and subsequently applied to data sets from UCT laboratory experiments.
Incomplete closure of mass balances was attributed to incorrect reaction stoichiometry inherited
through translation of the AQUASIM model into WEST®. The WEST® implementation of the
model to the experimental methanogenic systems gave fairly close correlations between
predicted and measured data for a single set of stoichiometric and kinetic constants, with
regressed hydrolysis rate constants. Application of the extended UCTADMI to experimental
sulphidogenic systems demonstrated simulation results reasonably close to measured data, with
the exception of effluent soluble COD and sulphate concentrations. Except for a single system
with a high COD:Sat ratio, sulphidogens are out competed for substrate by methanogens within
the model. Therefore the model does not properly represent the competition between
methanogenic and sulphidogenic organism groups.
Trends observed in application of the model to available pilot plant RSBR data were similar to
those observed in sulphidogenic systems, resulting in methanogens out-competing
sulphidogens. The model was used as a tool to explore various scenarios regarding operation of
the pilot plant. Based on the work conducted in this study, various areas for further information
and research were highlighted and recommended. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.
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Remoção da microalga Chlorella sorokiniana, cultivadas em fotobiorreatores, alimentados com efluente de reator anaeróbio tratando esgoto sintético, com emprego da técnica de ozonização seguida de flotação por ar dissolvido (FAD) / Removal of the microalgae Chlorella sorokiniana, grown in photobioreactor fed with anaerobic reactor effluent treating synthetic sewage, using the technique of ozonation followed by dissolved air flotation (DAF)Sahão, Thadeu Salin 14 June 2017 (has links)
O tratamento anaeróbio de esgoto doméstico em combinação com a produção de biomassa de algas é considerado uma excelente alternativa para a remoção de nutrientes. O processo de separação sólido-líquido de microalgas continua sendo um grande desafio técnico e econômico. A ozonização seguida de flotação por dissolvido é uma alternativa interessante visando a separação de microalgas e, consequentemente, a remoção de nutrientes. Os objetivos deste trabalho foram: avaliar a remoção de nitrogênio e fósforo de um efluente de reator anaeróbio através do crescimento da microalga Chlorella sorokiniana em fotobiorreator tipo flat panel e investigar o uso da ozonização associada à flotação por ar dissolvido para o processo de separação sólido-líquido da microalga Chlorella sorokiniana. O efluente anaeróbio foi obtido a partir de um reator anaeróbio com leito de fibras flexíveis que trata esgoto doméstico sintético. As microalgas foram cultivadas em fotobiorreator flat panel com tempo de cultivo de cinco dias, sob condições controladas: intensidade de luz (196 μmol m-2 s-1), fluxo de ar (0,2 vvm), temperatura (29 ± 1 °C) e fotoperíodo (12 horas com iluminação artificial e 12 horas no escuro). No final do período de cultivo, foram realizados ensaios para adequação da FAD e da ozonização, através da avaliação de parâmetros, tais como: dosagem de ozônio, dosagem de polímero, pH, tempos e gradientes de mistura rápida e floculação, velocidade de flotação e quantidade de ar necessária para flotação por ar dissolvido. O reator anaeróbio apresentou altas eficiências de remoção de demanda química de oxigênio e demanda bioquímica de oxigênio: 63 ± 6% e 53 ± 8%, respectivamente. Ao final do período de cultivo das microalgas no fotobiorreator, as remoções de nitrogênio total dissolvido e fósforo total dissolvido foram de 52,1% e 31,8%, respectivamente. Analisando os resultados referentes à etapa de separação sólido-líquido, verificou-se que o pH não influenciou significativamente na eficiência do tratamento; altas velocidades de flotação (24 cm.min-1 e 36 cm.min-1) podem ser empregadas; a etapa de floculação não contribuiu para melhora do tratamento; e a ozonização não contribuiu significativamente para a melhora da eficiência do processo de separação sólido-líquido. / Anaerobic treatment of wastewater in combination with the production of algae biomass is an excellent alternative for nutrient removal. The process of solid-liquid separation of microalgae remains a major technical and economic challenge. Ozonization followed by flotation by dissolved air is an interesting alternative for the separation of microalgae and removal of nutrients. The objectives of this work were: to evaluate the nitrogen and phosphorus removal of an anaerobic effluent through the growth of Chlorella sorokiniana microalgae in a flat panel photobioreactor and to investigate the use of ozonation associated with dissolved air flotation (DAF) for the solid-liquid separation of the microalga Chlorella sorokiniana. The anaerobic effluent was obtained from a fixed-bed anaerobic reactor with flexible fibers. The microalgae were grown in a flat panel photobioreactor for five days, under controlled conditions: light intensity (196 mol μm -2 s-1), Airflow (0.2 vvm), temperature (29 ± 1°C) and photoperiod (12 hours). At the end of the cultivation period, tests were carried out to adjust FAD and ozonization through the evaluation of parameters such as: ozone dosage, polymer dosage, pH, fast mixing and flocculation times and gradients, flotation velocity. The anaerobic reactor presented high efficiency of removal of COD and BOD, 63 ± 6% and 53 ± 8%, respectively. At the end of the microalgae culture period in the photobioreactor, the removal of total nitrogen, total phosphorus and total dissolved carbon of the effluent from the anaerobic reactor were 52.1%, 31.8% and 66.2%, respectively. Analyzing the results concerning the separation step, it was verified that the pH did not influence the removal efficiencies, high flotation rates can be employed in the separation process, the flocculation step in the treatment was not necessary and ozonation didnt contributed to an improvement the solid-liquid separation process.
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Treatment of biodiesel wastewater in a hybrid anaerobic baffled reactor microbial fuel cell (ABR-MFC) systemGrobbelaar, Loreen January 2019 (has links)
Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2019. / The biodiesel industry produces large volumes of biodiesel wastewater (BDWW) during the purification of crude biodiesel. This wastewater is characterised by high concentrations of chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), and fats, oils and greases (FOG) which in turn defines BDWW as a highly polluted effluent. The low nitrogen and phosphorous content of BDWW creates an unfavourable environment for the growth of microorganisms, thereby making it difficult to degrade naturally. Biodiesel companies discharge untreated non-compliant wastewater directly to the municipal sewer system. Treatment prior to discharge is a necessity since the disposal of untreated BDWW may raise serious environmental concerns (i.e. disturbance of biological ecosystems) resulting in penalties liable by non-compliant companies due to the implementation of the waste discharge charge system (WDCS) which is regulated by the industrial waste discharge standard limits in South Africa (SA).
This study aimed to combine the advantages of the conventional anaerobic baffled reactor (ABR) system with microbial fuel cell (MFC) technology resulting in an innovative technology used to treat high strength industrial BDWW at ambient conditions. Many studies have reported effective treatment of BDWW, however to date literature implementing an ABR equipped with MFC technology has not been reported.
The main objectives of the study were to determine which parameters do not meet the industrial wastewater discharge standard limits, whether pH and carbon:nitrogen:phosphorous (C:N:P) ratio adjustments will suffice prior to treatment with the ABR-MFC, the maximum power density (PD) as well as to determine the treatment efficiency of the ABR-MFC.
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Treatment of Wastewater Containing Sulfate by Vertical-Flow Constructed Wetlands.Chung, Chia-chi 22 July 2010 (has links)
The purpose of this study is to use vertical-flow constructed wetlands (VFCW) microcosm systems to investragte the removal efficiencies of sulfate. The system was located on the campus sewage treatment plant. nn National Sun Yat-sen University. In this study, two media, gravel and peat, were installed in four different systems. The two system with same media were separated into vegetated and non-vegetated (control) ones respectively. In the test runs, the operation methods included batch type filled with water, continuous flow and integrated vertical flow constructed wetland (IVCW) with continuous flow. In batch type test, it was run under an initial concentrations of SO42--S about 500 mg/L. The experimental results showed that the removal efficiencies were increased with increasing COD concentrations. Under the same conditions but with continuous flow operation, the removal efficiencies of SO42--S were lower than the batch type one, which 80% could be reached. The best system for operation was P1 (peat with vegetated), in which the removal effciency reached 90%. The experimental results also showed that the vegetated systems presented higher removal efficiencies of sulfate than the non-vegetated ones. In addition, this research were increased the concentrations of SO42--S and COD to about 1200 mg/L and 4000 mg/L respectively. The experimental results showed that the IVCW treatment system could achived greater efficiency than VFCW treatment system.
The experimental in depth research test run indicated that the anaerobic condition did not affect the removal efficiencies of ammonia by using batch type. However, nitrification was the main reaction of ammonia to nitrate in the continuous flow type systems. When ORP values were found below the -300 mV, the sulfate began to be drcreased. It was believed that if the anaerobic condition were well be established, while the organic carbon could be contented in this system, the sulfate reducing bacteria (SRB) might live, and then sulfate could be removed.
The effect of temperature on sulfate removal was generally established in this study. According to the experimental results, it was found that the activity of SRB motility was higher in higher temperature (35¢J) than that in lower temperature (25¢J).
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Anaerobic treatment of wastewater in a UASB reactorKorsak, Larisa January 2008 (has links)
<p>The anaerobic treatment of waste water has been studied with an emphasis on the Up- flow Anaerobic Sludge Blanket (UASB) reactor. A model to describe the processes occurring in a UASB reactor was developed and an experimental study of the anaerobic wastewater treatment systems in Nicaragua was also performed.</p><p>Experimental work was carried out in order to link the study to the wastewater treatment situation in Nicaragua, a developing country. In order to assess the performance of the treatment plants, the methanogenic activity of sludge from seven anaerobic wastewater treatment plants was first addressed. Due to a lack of Standards for the measurement of methanogenic activity, a laboratory method was developed based on the methods found in the literature. An additional aim of this study was to find adequate inoculum for the wastewater treatment plant in a brewery using an anaerobic reactor. Physic-chemical characteristics of the sludge were also determined to provide a basis for decisions regarding the agricultural employment of the sludge from the treatment plants.</p><p>A one-dimensional model describing the physical and biological processes occurring in an Up-flow Anaerobic Sludge Blanket reactor has been developed. These processes are advection, dispersion and reaction in the granule, including mass transport at the interface and diffusion within the particle. The advection-dispersion equation is used to describe these phenomena in the reactor. Dispersion is mainly caused by the gas bubbles rising up through the reactor and the granules in the ascending flow. The extent of the dispersion is expressed by the dimensionless Peclet (Pe) number. It is assumed that the biological degradation takes place at the surface and within the granules. The processes occurring in the granules formed by the microorganisms are described in detail; they include diffusion in the stagnant film around the granule, diffusion within the particle, and a degradation reaction. From these processes, the reaction term is analytically determined. The granules were modelled as spherical porous biocatalysts of different sizes. The biochemical degradation reactions were assumed to follow Monod type kinetics of the first order. For the numerical solution of the model, a standard program was used (Within MATLAB). The model was applied to some experimental data taken from the literature.</p><p>An important characteristic of the model is that it can simultaneously take into account reactions in granules of different sizes. At present, the parameters of the model are calculated using data from the literature; but experimental measurements of the main parameters are planned. The impact of the different parameters was studied by numerical simulation and its validity was tested using experimental data reported in the literature. The model could be a useful tool in the performance optimization of UASB reactors by predicting the influences of different operational parameters.</p>
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Evaluation of fluidised-bed reactors for the biological treatment of synthol reaction water, a high-strength COD petrochemical effluent / by Katharine Gaenor Aske SwabeySwabey, Katharine Gaenor Aske January 2004 (has links)
Reaction water, a high-strength COD (chemical oxygen demand) petrochemical effluent,
is generated during the Fischer-Tropsch reaction in the SASOL Synthol process at
SASOL SynFuels, Secunda, South Africa. Distillation of the reaction water to remove
non- and oxygenated hydrocarbons yields approximately 25 - 30 ML/d of an organic
(carboxylic) acid-enriched stream (average COD of 16 000 mg/L) containing primarily
C2 – C5 organic acids, light oils, aldehydes, ketones, cresols and phenols. Together with
the Oily sewer water (API) and Stripped Gas Liquor (SGL) process streams, this process
effluent is currently treated in ten dedicated activated sludge basins. However, the
successful operation of these activated sludge systems has proven to be difficult with low
organic loading rates (3.5 kg COD/m3.d) low COD removal efficiencies (<80 %) and
high specific air requirements (60 - 75 m3 air/kg CODrem). It is hypothesised that these
operational difficulties can be attributed to organic shock loadings, variation in
volumetric and hydraulic loadings, as well as variations in the composition of the various
process streams being treated. Due to the fact that the Fischer-Tropsch (Synthol) reaction
water constitutes 70 % of the COD load on the activated sludge systems, alternative
processes to improve the treatment cost and efficiency of the Fischer-Tropsch acid stream
are being investigated. Various studies evaluating the aerobic and anaerobic treatment of
Fischer-Tropsch reaction water alone in suspended growth wastewater treatment systems
have proven unsuccessful. High rate fixed-film processes or biofilm reactors, of which
the fluidised-bed reactors are considered to he one of the most effective and promising
processes for the treatment of high-strength industrial wastewaters, could he a suitable
alternative. The primary aim of this study was to evaluate the suitability of biological
fluidised-bed reactors (BFBRs) for the treatment of Fischer-Tropsch reaction water.
During this study, the use of aerobic and anaerobic biological fluidised-bed reactors
(BFBR), using sand and granular activated carbon (GAC) as support matrices, were
evaluated for the treatment of a synthetic effluent analogous to the Fischer-Tropsch
reaction water stream. After inoculation, the reactors were operated in batch mode for 10
days at a bed height expansion of 30% and a temperature of 30 ºC to facilitate biofilm
formation on the various support matrices. This was followed by continuous operation of
the reactors at hydraulic retention times (HRTs) of 2 days. While the COD of the
influent and subsequent organic loading rate (OLR) was incrementally increased from 1
600 mg/L to a maximum of 20 000 mg/L and 18 000 mg/L for the aerobic and anaerobic
reactors, respectively. Once the maximum influent COD concentration had been
achieved the OLR was further increased by decreasing the HRTs of the aerobic and
anaerobic reactors to 24h and 8h, and 36h, 24h and 19h, respectively. The dissolved
O2 concentration in the main reactor columns of the aerobic reactors was constantly
maintained at 0.50 mg/L.
Chemical Oxygen Demand (COD) removal efficiencies in excess of 80 % at OLR of up
to 30 kg COD/m3.d were achieved in the aerobic BFBRs using both sand and GAC as
support matrices. Specific air requirements were calculated to be approximately 35 and
41 m3 air/kg CODrem for the BFBRs using sand and GAC as support matrices,
respectively. The oxygen transfer efficiency was calculated to be approximately 5.4 %.
At high OLR (> 15 kg COD/m3.d) significant problems were experienced with plugging
and subsequent channelling in the BFBR using GAC as support matrix and the reactor had
to be backwashed frequently in order to remove excess biomass. Despite these backwash
procedures, COD removal efficiencies recovered to previous levels within 24 hours. In
contrast, no significant problems were encountered with plug formation and channelling
in the BFBR using sand as support matrix. In general the overall reactor performance
and COD removal efficiency of the aerobic BFBR using sand as support matrix was more
stable and consistent than the BFBR using GAC as support matrix. This BFBR was also
more resilient to variations in operational conditions, such as the lowering of the
hydraulic retention times and changes in the influent pH. Both aerobic reactors displayed
high resilience and COD removal efficiencies in excess of 80 % were achieved during
shock loadings. However, both reactors were highly sensitive to changes in pH and any
decrease in pH below the pKa values of the volatile fatty acids in the influent (pKa of
acetic acid = 4.76) resulted in significant reductions in COD removal efficiencies.
Maintenance of reactor pH above 5.0 was thus an essential facet of reactor operation.
It has been reported that the VFA/alkalinity ratio can be used to assess the stability of
biological reactors. The VFA/alkalinity ratios of the aerobic BFBRs containing sand and
GAC as support matrices were stable (VFNalkalinity ratios of < 0.3 - 0.4) until the OLR
increased above 10 kg/m3.d. At OLRs higher than 10 kg/m3.d the VFA/alkalinity ratios
in the BFBR using sand support matrix increased to 4, above the failure limit value of 0.3
- 0.4. In contrast the VFA/alkalinity ratios of the BFBR using GAC support matrix
remained stable until an OLR of 15 kg/m3.d was obtained, where the VFA/alkalinity
ratios then increased to > 3. Towards the end of the study when an OLR of
approximately 25 kg/m3.d was obtained the VFA/alkalinity ratios of both the BFBRs
using sand and GAC as support matrices increased to 9 and 6 respectively, indicating the
decrease in reactor stability and acidification of the process. Total solid (TS) and volatile
solid (VS) concentrations in the aerobic BFBRs were initially high and decreased over
time. While the total suspended solids (TSS) and volatile suspended solids (VSS)
concentrations were initially low and increased over time as the OLR was increased, this
is thought to be as a result of decreased HRT leading to biomass washout.
The anaerobic BFBR using sand as support matrix never stabilised and COD removal
efficiency remained very low (< 30 %), possibly due to the high levels of shear forces.
Further studies concerning the use of sand as support matrix were subsequently
terminated. An average COD removal efficiency of approximately 60 % was achieved in
the anaerobic BFBR using GAC as a support matrix at organic loading rates lower than
10 kg COD/m3.d. The removal efficiency gradually decreased to 50 % as organic loading
rates were increased to 20 kg COD/m3.d. At OLRs of 20 kg COD/m3.d, the biogas and
methane yields of the anaerobic BFBR using GAC as support matrix were determined to
be approximately 0.38 m3 biogas/kg CODrem (0.3 m3 biogas/m3reactor vol.d), and 0.20 m3
CH4/kg CODrem (0.23 m3 CH4/m3reactor vol.d), respectively. This value is 57 % of the
theoretical maximum methane yield attainable (3.5 m3 CH4/kg CODrem). The methane
yield increased as the OLR increased, however, when the OLR reached 8 kg/m3.d the
methane yield levelled off and remained constant at approximately 2 m3 CH4/m3reactor vol.d.
Although the methane content of the biogas was initially very low (< 30 %), the methane
content gradually increased to 60 % at OLRs of 20 kg COD/m3.d. The anaerobic BFBR
using GAC as support matrix determined that as the OLR increased (>12 kg/m3.d), the
VFA/alkalinity ratio increased to approximately 5, this is indicative of the decrease in
stability and acidification of the process. The anaerobic BFBR using GAC as support
matrix experienced no problems with plug formation and channelling. This is due to the
lower biomass production by anaerobic microorganisms than in the aerobic reactors. The
TS and VS concentrations were lower than the aerobic concentrations but followed the
same trend of decreasing over time, while the TSS and VSS concentrations increased due
to decreased HRTs. The anaerobic BFBR was sensitive to dramatic variations in organic
loading rates, pH and COD removal efficiencies decreased significantly after any shock
loadings.
Compared to the activated sludge systems currently being used for the biological
treatment of Fischer-Tropsch reaction water at SASOL SynFuels, Secunda, South Africa,
a seven-fold increase in OLR and a 55 % reduction in the specific air requirement was
achieved using the aerobic BFBRs. The methane produced could also be used as an
alternative source of energy. It is, however, evident that the support matrix has a
significant influence on reactor performance. Excellent results were achieved using sand
and GAC as support matrices in the aerobic and anaerobic BFBRs, respectively. It is
thus recommended that future research be conducted on the optimisation of the use of
aerobic and anaerobic BFBRs using these support matrices.
Based on the results obtained from this study, it can be concluded that both aerobic and
anaerobic treatment of a synthetic effluent analogous to the Fischer-Tropsch reaction
water as generated by SASOL in the Fischer-Tropsch Synthol process were successful
and that the application of fluidised-bed reactors (attached growth systems) could serve
as a feasible alternative technology when compared to the current activated sludge
treatment systems (suspended growth) currently used.
Keywords: aerobic treatment, anaerobic treatment, biological fluidised-bed reactors,
petrochemical effluent, Fischer-Tropsch reaction water, industrial wastewater. / Thesis (M. Omgewingswetenskappe)--North-West University, Potchefstroom Campus, 2004.
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Process development for co-digestion of toxic effluents : development of screening proceduresDlamini, Sithembile January 2009 (has links)
Submitted in partial fulfillment of academic requirements for the degree of Masters of Technology: Department of Chemical Engineering, Durban University of Technology, 2009. / The primary objective of this project was to establish a screening protocol which could be used
to access high strength/toxic effluent for toxicity and degradability prior to being disposed in
wastewater treatment works.
The serum bottle method (materials and method section) is simple, makes use of small glass vials
(125 mℓ-volume were used in this research) which do not require any stirring nor feeding device
or other engineered tool: a serum bottle is sealed immediately after all components are poured
inside and thereafter conducted in a batch mode and occasionally shaken to ensure adequate
homogenisation of the components. The only variables which are regularly measured are the
volume of biogas produced and gas composition. The two assays, originally developed by
Owen et al. (1979) to address the toxicity and the biodegradability have been combined in a
single test called AAT, Anaerobic Activity Test, which enables one to assess simultaneously the
inhibitory effect on the methanogenic biomass and the biodegradability of the test material as
well as the ability of the biomass to adapt to the test material and therefore to overcome the
initial inhibition.
The screening protocol is illustrated in Annexure A. The protocol consists of a sequence of
assays which employ the serum bottle methodology. A first step of the procedure is aimed at
rapidly estimating whether the effluent is potentially toxic to the methanogenic biomass and in
what concentration. The second step is a more extensive screening, aimed at precisely
characterising the toxicity of the effluent, the extent of biodegradation that can be achieved, as
well as at establishing whether a potential for adaptation of the biomass exists upon exposure. If
the sample passes the screening stage, the same serum bottle method will be used to conduct a
series of batch co-digestion experiments aimed at evaluating a convenient volumetric ratio
between the test material and the readily biodegradable substrate. Finally, a laboratory-scale codigestion
trial could simulate the full-scale process, thus enabling the selection of appropriate
operating conditions for the start-up of the full-scale implementation.
This the protocol has been used to assess the amenability to be anaerobically (co)digested of four
industrial effluents, i.e. size and distillery effluents which are classified as high strength and
scour and synthetic dye effluents classified as toxic. From the biodegradability and toxicity
assays the following conclusions were drawn. The size and distillery effluent were found to be
ii
degradable at 32 g COD/ℓ and 16 g COD /ℓ concentrations respectively. Concentrations higher
than these stipulated above were found inhibitory. Scour effluent was found to be recalcitrant at
all concentration tested and synthetic dye was 100 % degradable at 0.12 g COD/ℓ and lower and
highly inhibitory at concentration higher than 1.1 g COD/ℓ.
Co-digestion experiment using serum bottle AAT method were undertaken between effluents i.e.
size + distillery, size + scour, distillery + synthetic dye in an attempt to verify whether the
digestion performance benefits from simultaneous presence of the two substrates. The volumetric
ratios between the effluents were 1:1, 1:2, 2:1. The presence of two mixtures in the case of size
and distillery had better methane production compared to individual substrate i.e. size or
distillery separate. The mixture with volumetric flow rate ratio of 2:1 (size: distillery) was
preferable in terms of process performance as it had highest COD removal compared to the other
mixtures /ratios and individual substrates. The mixture of size and scour (2:1) had highest
degradation percentage compared to other ratios but not high enough to qualify as degradable
(less than 50 %). The mixture of distillery and synthetic dye had the same pattern with ratio of
2:1 giving the best COD conversion. The pattern than can be drawn from the degradability of
mixtures is: the degradability of mixtures increase with the increasing amount of the most
biodegradable compound/effluent in the mixture.
Serum bottle results provided the detailed information regarding the safe operating parameters
which should be used during the starting point for the larger scale investigation i.e. lab-scale
investigations. The lab scale investigations were conducted primarily to validate screening and
monitor how the digestion progresses and also to provide data for future project i.e. pilot plant
investigation. Other effluents i.e. scour and synthetic dye and their co-digestion mixture were
excluded from the lab-scale investigations since they were found to be non- biodegradable i.e.
their COD conversion was less the 50 % in the screening protocol. Due to time constrains and
other technical difficulties in the laboratory, the co-digestion of size and distillery mixture trials
we not conducted on the laboratory scale.
Laboratory-scale digestion trials showed that the best organic loading rate for distillery effluent
in terms of reactor performance and stability was 1.0g COD/ℓ with efficiency of about 45 %, and
for size was 2.0g COD/ℓ with an efficiency of 40 %. The efficiencies obtained in both effluents
trials could be greatly improved by acclimation; however these results showed that the digestion
of these effluents on the bigger scale is possible.
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