Enhanced biodegradation of phenolic compounds in landfill leachate by enriched nitrifying membrane bioreactor sludge

Which biofilm reactor is suitable for degradation of 2,4-dimethylphenol, focusing on bacteria, algae, or a combination of bacteria-algae?

Effectively treating phenolic substances is a crucial task in environmental protection. This study aims to determine whether bacterial-algae biofilm reactors offer superior treatment efficacy compared to traditional activated sludge and biofilm reactors. The average degradation ratios of 2,4-dimethylphenol (40, 70, 150, 300, and 230 mg/L) were found to be 98 %, 99 %, 92.1 %, 84.7 %, and 63.7 % respectively. The bacterial-algae biofilm demonstrates a higher tolerance to toxicity, assimilation ability, and efficacy recovery ability. The cell membrane of Chlorella in the bacteria-algae biofilm is not easily compromised, thus ensuring a stable pH environment. High concentrations of tightly bound extracellular polymers (TB-EPS) enhance the efficacy in treating toxic pollutants, promote the stable structure. Intact Chlorella, bacilli, and EPS were observed in bacterial-algal biofilm. The structural integrity of bacteria-algae consistently enhances its resistance to the inhibitory effects of high concentrations of phenolic compounds. Cloacibacterium, Comamonas, and Dyella were the main functional bacterial genera that facilitate the formation of bacterial-algal biofilms and the degradation of phenolic compounds. The dominant microalgal families include Aspergillaceae, Chlorellales, Chlorellaceae, and Scenedesmaceae have certain treatment effects on phenolic substances. Chlorellales and Chlorellaceae have the ability to convert NH4+-N. The Aspergillaceae is also capable of generating synergistic effects with Chlorellales, Chlorellaceae, and Scenedesmaceae, thereby establishing a stable bacterial-algal biofilm system.

Laccase encapsulation immobilized in mesoporous ZIF-8 for enhancement bisphenol A degradation

Endocrine disruptors (EDCs) such as bisphenol A (BPA) have many adverse effects on environment and human health. Laccase encapsulation immobilized in mesoporous ZIF-8 was prepared for efficient degradation of BPA. The ZIF-8 (PA) with highly ordered mesopores was synthesized using trimethylacetic acid (PA) as a template agent. On account of the improvement of skeletal stability by cross-linking agent glutaraldehyde, ZIF-8 (PA) realized laccase (FL) immobilization within the mesopores through encapsulation strategy. By replacing the template agent, the effect of pore size on the composite activity and immobilization efficiency by SEM characterization and kinetic analysis were investigated. Based on the physical protection of ZIF-8(PA) on laccase, as well as electrostatic interactions between substances and changes in surface functional groups (e.g. -OH, etc.), multifaceted enhancement including activity, stability, storability were engendered. FL@ZIF-8(PA) could maintain high activity in complex systems at pH 3-11, 10-70 °C or in organic solvent containing system, which exhibited an obvious improvement compared to free laccase and other reported immobilized laccase. Combined with TGA, FT-IR and Zeta potential analysis, the intrinsic mechanism was elaborated in detail. On this basis, FL@ZIF-8(PA) achieved efficient removal of BPA even under adverse conditions (removal rates all above 55% and up to 90.28%), and was suitable for a wide range of initial BPA concentrations. Combined with the DFT calculations on the adsorption energy and differential charge, the mesoporous could not only improve the enrichment performance of BPA on ZIFs, but also enhance the interaction stability. Finally, FL@ZIF-8(PA) was successfully applied to the degradation of BPA in coal industry wastewater. This work provides a new and ultra-high performances material for the organic pollution treatment in wastewater.

Feasibility of implementing quorum quenching technology to mitigate membrane fouling in MBRs treating phenol-rich pharmaceutical wastewater: Application of Rhodococcus sp. BH4 and quorum quenching consortium

This study aimed to implement quorum quenching (QQ) to mitigate membrane fouling in membrane bioreactors (MBRs) treating phenol-rich pharmaceutical wastewater using Rhodococcus sp. BH4 and isolated QQ consortium (QQcs) from activated sludge. Neither BH4 nor QQcs impacted the removal efficiency of chemical oxygen demand (COD) (>94%), phenol (>99%), and ammonium (>99%), indicating that QQ did not have adverse impact on treatment performance. In addition, both BH4 and QQcs effectively retarded membrane fouling, which could be attributed to the reduction of soluble microbial products (SMP). Interestingly, the TMP increase was delayed 68.7% by Rhodococcus sp. BH4, while 31.3% was achieved by QQcs. This difference may be due to the relatively higher degradation for short- and medium-chain N-acyl-homoserine lactones (AHLs) by BH4 compared to the QQcs. Furthermore, the possible presence of quorum sensing (QS) bacteria within QQcs also could have contributed to the less effective fouling control than that of BH4.

Occurrence of organic micropollutants in municipal landfill leachate and its effective treatment by advanced oxidation processes

Landfilling is the most prominently adopted disposal technique for managing municipal solid waste across the globe. However, the main drawback associated with this method is the generation of leachate from the landfill site. Leachate, a highly concentrated liquid consisting of both organic and inorganic components arises environmental issues as it contaminates the nearby aquifers. Landfill leachate treatment by conventional methods is not preferred as the treatment methods are not much effective to remove these pollutants. Advanced oxidation processes (AOPs) based on both hydroxyl and sulfate radicals could be a promising method to remove the micropollutants completely or convert them to non-toxic compounds. The current review focuses on the occurrence of micropollutants in landfill leachate, their detection methods and removal from landfill leachate using AOPs. Pharmaceuticals and personal care products occur in the range of 10^-1 to more than 100 μg L^-1 whereas phthalates were found below the detectable limit to 384 μg L^-1, pesticides in the order of 10^-1 μg L^-1 and polyaromatic hydrocarbons occur in concentration from 10^-2 to 114.7 μg L^-1. Solid-phase extraction is the most preferred method for extracting micropollutants from leachate and liquid chromatography (LC) - mass spectrophotometer (MS) for detecting the micropollutants. Limited studies have been focused on AOPs as a potential method for the degradation of micropollutants in landfill leachate. The potential of Fenton based techniques, electrochemical AOPs and ozonation are investigated for the removal of micropollutants from leachate whereas the applicability of photocatalysis for the removal of a wide variety of micropollutants from leachate needs in-depth studies.

Emerging materials and technologies for landfill leachate treatment: A critical review

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Effect of sludge recirculation on removal of antibiotics in two-stage membrane bioreactor (MBR) treating livestock wastewater

Two-stage MBR consisting of anaerobic and aerobic reactors was operated at total hydraulic retention time (HRT) of 48 h for the treatment of livestock wastewater containing antibiotics, i.e. amoxicillin (AMX), tiamulin (TIA), and chlortetracycline (CTC), under the (1st) absence and (2nd) presence of sludge recirculation between the reactors. During the operation with sludge recirculation, the removals of organic and nitrogen were enhanced. Meanwhile, the removals of TIA and CTC were found to decrease by 9% and 20% in the aerobic reactor but increased by 5% to 7% in the anaerobic reactor due to the relocation of biomass from the aerobic to the anaerobic reactor. A high degree of AMX biodegradation under both anaerobic and aerobic conditions and partial biodegradation of TIA and CTC under aerobic conditions were confirmed in batch experiments. Moreover, the effect of sludge recirculation on biomass and pollutant removal efficiencies in the 2-stage MBR was revealed using microbial community analyses. Membrane filtration also helped to retain the adsorbed antibiotics associated with small colloidal particles in the system.

Effect of leachate effluent from activated sludge and membrane bioreactor systems with acclimatized sludge on plant seed germination

This research comparatively investigates the effect of landfill leachate effluent of two biological treatment schemes on germination of Lactuca sativa and Vigna radiata. The treatment schemes are two-stage activated sludge (AS) and two-stage membrane bioreactor (MBR) systems with acclimatized seed sludge. The AS and MBR are operated under two concentrations of landfill leachate influent: moderate (condition 1) and elevated (condition 2). The results show that, under condition 1, the AS and MBR efficiently remove 80-96% of organic compounds and nutrients and 81-100% of harmful micropollutants. Under condition 2 with elevated influent concentration, MBR is more effective in biodegrading micropollutants than the AS system. The germination rate (GR) and germination seed index (GSI) of L. sativa and V. radiata germinated with AS and MBR effluent from condition 1 are 100% and 1.29-1.56. Under condition 2, the GR and GSI with AS effluent are reduced to 80% and 0.65-0.77, while those with MBR effluent are 100% and 1.27-1.38. Quantitative real-time polymerase chain reaction (qPCR) analysis indicates that the bacterial community in the MBR is more abundant than in the AS, especially ammonia oxidizing bacteria, Nitrobacter, and Nitrospira, which aid heterotrophic bacteria in biodegradation of micropollutants and promote the growth of heterotrophs. The bacterial abundance and community composition render the MBR scheme more operationally suitable for elevated landfill-leachate influent concentrations. By comparison, the MBR system is more effective in removal of micropollutants than the AS, as evidenced by higher GR and GSI. The technology also could potentially be applied to water reclamation. A lack of technological and financial resources in many developing countries nevertheless precludes the adoption of MBR despite higher pollutant removal efficiency. An alternative solution is the use of acclimatized seed sludge in AS system to enhance treatment efficiency, especially in influent with low concentrations of micropollutants. In addition, the seed germination results suggest the possibility of water reuse in agriculture.

The Impact of Exogenous Aerobic Bacteria on Sustainable Methane Production Associated with Municipal Solid Waste Biodegradation: Revealed by High-Throughput Sequencing

In this work, the impact of exogenous aerobic bacteria mixture (EABM) on municipal solid waste (MSW) is well evaluated in the following aspects: biogas production, leachate analysis, organic waste degradation, EABM population, and the composition of microbial communities. The study was designed and performed as follows: the control bioreactor (R1) was filled up with MSW and the culture medium of EABM and the experimental bioreactor (R2) was filled up with MSW and EABM. The data suggests that the composition of microbial communities (bacterial and methanogenic) in R1 and R2 were similar at day 0, while the addition of EABM in R2 led to a differential abundance of Bacillus cereus, Bacillus subtilis, Staphylococcus saprophyticus, Staphlyoccus xylosus, and Pantoea agglomerans in two bioreactors. The population of exogenous aerobic bacteria in R2 greatly increased during hydrolysis and acidogenesis stages, and subsequently increased the degradation of volatile solid (VS), protein, lipid, and lignin by 59.25%, 25.68%, 60.47%, and 197.62%, respectively, compared to R1. The duration of hydrolysis and acidogenesis in R2 was 33.33% shorter than that in R1. At the end of the study, the accumulative methane yield in R2 (494.4 L) was almost three times more than that in R1 (187.4 L). In addition, the abundance of acetoclasic methanogens increased at acetogenesis and methanogenesis stages in both bioreactors, which indicates that acetoclasic methanogens (especially Methanoseata) could contribute to methane production. This study demonstrates that EABM can accelerate organic waste degradation to promote MSW biodegradation and methane production. Moreover, the operational parameters helped EABM to generate 20.85% more in accumulative methane yield. With a better understanding of how EABM affects MSW and the composition of bacterial community, this study offers a potential practical approach to MSW disposal and cleaner energy generation worldwide.

Removal and transformation pathways of benzothiazole and benzotriazole in membrane bioreactors treating synthetic municipal wastewater

Lab-scale membrane bioreactors (MBRs), with aerated activated sludge and internal microfiltration module, were used for the treatment of municipal wastewater containing high, yet environmentally relevant, concentrations of benzothiazole (BT) and benzotriazole (BTA). These high production volume compounds are commonly used in the industry and households, and therefore occur ubiquitously in municipal wastewater and the aquatic environment. The aim of this study was to assess the removal of BT and BTA from synthetic municipal wastewater in MBRs and to estimate the contribution of elimination processes and to identify potential biotransformation products. The overall removal of BT and BTA was high, and after the adaptation period, it reached 99.8% and 97.2%, respectively, but recurring periods of unstable BTA removal occurred. The removal due to biotransformation was 88% for BT and 84% for BTA and the disposal with waste sludge accounted for only <1% of the removed load. The remaining fraction of the removed load of BT and BTA was attributed to be retained by phenomena associated with membrane fouling. The adaptation process was reflected in multifold increase in biodegradation kinetic coefficient (k_biol) for BT (reported for the first time) and BTA. Biodegradation was attributed to catabolic mechanism rather than to cometabolism. Hydroxylation was observed to be the main transformation reaction for BT, whereas for BTA hydroxylation, methylation and cleavage of benzene ring were noted. This study has shown the feasibility of treating municipal wastewater with high concentrations of BT and BTA in MBRs and identified potential challenges for the removal of BTA.

Membrane bioreactors and electrochemical processes for treatment of wastewaters containing heavy metal ions, organics, micropollutants and dyes: Recent developments

Research and development activities on standalone systems of membrane bioreactors and electrochemical reactors for wastewater treatment have been intensified recently. However, several challenges are still being faced during the operation of these reactors. The current challenges associated with the operation of standalone MBR and electrochemical reactors include: membrane fouling in MBR, set-backs from operational errors and conditions, energy consumption in electrochemical systems, high cost requirement, and the need for simplified models. The advantage of this review is to present the most critical challenges and opportunities. These challenges have necessitated the design of MBR derivatives such as anaerobic MBR (AnMBR), osmotic MBR (OMBR), biofilm MBR (BF-MBR), membrane aerated biofilm reactor (MABR), and magnetically-enhanced systems. Likewise, electrochemical reactors with different configurations such as parallel, cylindrical, rotating impeller-electrode, packed bed, and moving particle configurations have emerged. One of the most effective approaches towards reducing energy consumption and membrane fouling rate is the integration of MBR with low-voltage electrochemical processes in an electrically-enhanced membrane bioreactor (eMBR). Meanwhile, research on eMBR modeling and sludge reuse is limited. Future trends should focus on novel/fresh concepts such as electrically-enhanced AnMBRs, electrically-enhanced OMBRs, and coupled systems with microbial fuel cells to further improve energy efficiency and effluent quality.

Removals of pharmaceutical compounds at different sludge particle size fractions in membrane bioreactors operated under different solid retention times

Removals of 10 pharmaceutical compounds by microbial sludge in membrane bioreactors (MBR) operated under infinite and limited solid retention time (SRT) were investigated. High removal (>80%) of DCF, TMP, NPX, IBP, and TCS were achieved but CBZ removals were low (<20%). The residual pharmaceutical compounds leftover from the biodegradation in different sludge particle size fractions was quantified through physical separation and filtration in series. The results revealed that hydrophobic compounds were mainly adsorbed onto the coarse particles (>0.45μm) where majority of adsorption site was available. Meanwhile, hydrophilic and moderate hydrophobic compounds were less associated with particles and they were retained in fine particles and gel-like substances (1 kDa-0.45μm). Most of the studied pharmaceutical compounds associated with fine particles and gel-like substances was subsequently rejected by membrane filtration in the MBRs. The operation of the MBR at high mixed liquor suspended solids concentration under long sludge age conditions could enhance the removals of pharmaceutical compounds through increased adsorption site on the sludge particles.

Roles of ammonia-oxidizing bacteria in improving metabolism and cometabolism of trace organic chemicals in biological wastewater treatment processes: A review

While there has been a significant recent improvement in the removal of pollutants in natural and engineered systems, trace organic chemicals (TrOCs) are posing a major threat to aquatic environments and human health. There is a critical need for developing potential strategies that aim at enhancing metabolism and/or cometabolism of these compounds. Recently, knowledge regarding biodegradation of TrOCs by ammonia-oxidizing bacteria (AOB) has been widely developed. This review aims to delineate an up-to-date version of the ecophysiology of AOB and outline current knowledge related to biodegradation efficiencies of the frequently reported TrOCs by AOB. The paper also provides an insight into biodegradation pathways by AOB and transformation products of these compounds and makes recommendations for future research of AOB. In brief, nitrifying WWTFs (wastewater treatment facilities) were superior in degrading most TrOCs than non-nitrifying WWTFs due to cometabolic biodegradation by the AOB. To fully understand and/or enhance the cometabolic biodegradation of TrOCs by AOB, recent molecular research has focused on numerous crucial factors including availability of the compounds to AOB, presence of growth substrate (NH₄-N), redox potentials, microorganism diversity (AOB and heterotrophs), physicochemical properties and operational parameters of the WWTFs, molecular structure of target TrOCs and membrane-based technologies, may all significantly impact the cometabolic biodegradation of TrOCs. Still, further exploration is required to elucidate the mechanisms involved in biodegradation of TrOCs by AOB and the toxicity levels of formed products.

Membrane-based separation of potential emerging pollutants

The potential emerging pollutants (PEPs) such as hazardous chemicals, toxic metals, bio-wastes, etc., pose a severe threat to human health, hygiene and ecology by way of polluting the environment and water sources. The PEPs are originated from various industrial effluent discharges including pharmaceutical, food and metal processing industries. These PEPs in contact with water may pollute the water and disturb the aquatic life. Innumerable methods have been used for the treatment of effluents and separating the toxic chemicals/metals. Of these methods, membrane-based separation processes (MBSPs) are effective over the conventional techniques for providing clean water from wastewater streams at an affordable cost with minimum energy requirement. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) methods as well as hybrid technologies are discussed citing the published results of the past decade.

Long-Term Performance of a Full-Scale Membrane Plant for Landfill Leachate Pretreatment: A Case Study

This paper presents a case study describing a full-scale membrane bioreactor (MBR) for the pretreatment of landfill leachates. The treatment train includes an aerated equalization tank, a denitrification tank, an oxidation/nitrification tank, and two ultrafiltration units. The plant has worked continuously since 2008 treating landfill leachates at a flux of 2⁻11 L·h-1·m-2. The old train of membranes worked in these conditions for more than seven years prior to being damaged and replaced. The permeability (K) of the membrane varied between 30 and 80 L·h-1·m-2·bar-1 during the years of operation. In 2010, after two years of operation, the oxidation/nitrification tank was changed to work in alternate cycles of aerated and anoxic conditions, in order to improve the denitrification process. The MBR, working at a mean sludge retention time of 144 days and with mixed liquor suspended solids of 17 g/L, achieved high removal rates of conventional contaminants, with more than 98% for Biochemical Oxygen Demand, 96% for ammonium, and 75% for Chemical Oxygen Demand (COD). From the COD balance, half the COD entering was determined to be biologically oxidized into carbon dioxide, while another 24% remains in the sludge. In order to obtain these results, the company used 5.2 KWh·m-3, while spending 0.79 €·m-3.

Use of aged sludge bioaugmentation in two-stage activated sludge system to enhance the biodegradation of toxic organic compounds in high strength wastewater

This research investigates the toxic organic compounds biodegradation efficiency of two-stage activated sludge systems with (bioaugmented) and without aged sludge bioaugmentation (non-bioaugmented). The influent was a mixture of leachate and agriculture wastewater (1:1, v/v), used as the representative high strength wastewater. The bioaugmented and non-bioaugmented systems were operated in parallel, with three levels (low, moderate, and high) of concentrations of organics, nitrogen, and toxic organic compounds in the influent (conditions 1, 2, and 3). The results showed that both systems could efficiently degrade the organic compounds. Nevertheless, the toxic organic compounds biodegradation efficiency of the bioaugmented system was higher than that of the non-bioaugmented one. The bioaugmentation enhanced the overall removal efficiency under conditions 1 and 2. However, the bioaugmented system became less effective under condition 3. Further analysis indicated that the bacterial groups essential to the toxic organic compounds biodegradation were abundant in the aged sludge, including heterotrophic bacteria, heterotrophic nitrifying bacteria, and nitrifying bacteria. The abundance of the effective bacteria improved the biodegradation and wastewater treatment performance of the bioaugmented system. In essence, the aged sludge bioaugmentation is a viable and eco-friendly solution to improving the treatment efficiency of the biological activated sludge system, despite limited biodegradation efficiency in an elevated compounds-concentration environment.

Review on landfill leachate treatment by electrochemical oxidation: Drawbacks, challenges and future scope

Various studies on landfill leachate treatment by electrochemical oxidation have indicated that this process can effectively reduce two major pollutants present in landfill leachate; organic matter and ammonium nitrogen. In addition, the process is able to enhance the biodegradability index (BOD/COD) of landfill leachate, which make mature or stabilized landfill leachate suitable for biological treatment. The elevated concentration of ammonium nitrogen especially observed in bioreactor landfill leachate can also be reduced by electrochemical oxidation. The pollutant removal efficiency of the system depends upon the mechanism of oxidation (direct or indirect oxidation) which depends upon the property of anode material. Applied current density, pH, type and concentration of electrolyte, inter-electrode gap, mass transfer mode, total anode area to volume of effluent to be treated ratio, temperature, flow rate or flow velocity, reactor geometry, cathode material and lamp power during photoelectrochemical oxidation may also influence the system performance. In this review paper, past and present scenarios of landfill leachate treatment efficiencies and costs of various lab scale, pilot scale electrochemical oxidation studies asa standalone system or integrated with biological and physicochemical processes have been reviewed with the conclusion that electrochemical oxidation can be employed asa complementary treatment system with biological process for conventional landfill leachate treatment as well asa standalone system for ammonium nitrogen removal from bioreactor landfill leachate. Furthermore, present drawbacks of electrochemical oxidation process asa landfill leachate treatment system and relevance of incorporating life cycle assessment into the decision-making process besides process efficiency and cost, have been discussed.

The fate of trace organic contaminants in sewage sludge during recuperative thickening anaerobic digestion

The aim of this work was to study the fate of trace organic contaminants (TrOCs) in sewage sludge during recuperative thickening anaerobic digestion. Sludge shearing at 3142s^-1 for 5minutes improved biogas production. By contrast, shearing at ≥6283s^-1 for 5minutes caused a notable reduction in biogas production and the removal of volatile solids. Results reported here showed the prevalent occurrence of 17 TrOCs in sewage sludge and highlights the importance of assessing TrOC removal via mass balance calculation by taking into account partitioning between the aqueous and solid phase as well as biodegradation. Hydrophilic and readily-biodegradable TrOCs (caffeine, trimethoprim, and paracetamol) were well removed and were not affected by shearing. TrOCs such as carbamazepine, gemfibrozil, and diuron showed biodegradation only at high shearing. It is possible that shearing can facilitate the circulation of TrOCs between aqueous and solid phases, thus, enhancing the biodegradation of some TrOCs.

Toxic compounds biodegradation and toxicity of high strength wastewater treated under elevated nitrogen concentration in the activated sludge and membrane bioreactor systems

This research has assessed the removal efficiencies of toxic compounds in the high strength wastewater (the leachate and agriculture wastewater mixture) using the activated sludge (AS) and membrane bioreactor (MBR) technologies under two carbon to nitrogen (C/N) ratios (C/N 14 and 6) and two toxic compounds concentrations (8-396μg/L and 1000μg/L). In addition, the toxicity evaluations of the AS and MBR effluents to the aquatic environment were undertaken at five effluent dilution ratios (10, 20, 30, 50 and 70% v/v). The findings indicate that the AS treatment performance could be enhanced by the elevation of the nitrogen concentration. Specifically, the C/N 6 environment helps promote the bacterial growth, particularly heterotrophic nitrifying bacteria (HNB) and nitrifying bacteria (NB), which produce the enzymes crucial to the toxic compounds degradation. The improved biodegradation makes the effluents less toxic to the aquatic environment, as evidenced by the lower mortality rates of both experimental fish species raised in the nitrogen-elevated diluted AS effluents. On the other hand, the elevated nitrogen concentration minimally enhances the MBR treatment performance, given the fact that the MBR technology is in itself a biological treatment scheme with very high compounds removal capability. Despite its lower toxic compounds removal efficiency, the AS technology is simple, inexpensive and operationally-friendly, rendering the system more applicable to the treatment operation constrained by the financial, manpower and technological considerations.