Conventional Activated Sludge Process Research Articles

Performance assessment of a modified trickling filter and conventional activated sludge process along with tertiary treatment in removing emerging pollutants from urban sewage

The absence of effective wastewater treatment technology to eliminate emerging pollutants from municipal sewage has become a pressing issue. In this study, the efficacy of a novel modified trickling filter (MTF), conventional activated sludge process (ASP) and two tertiary systems (UV and ozonation) were compared in eliminating antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs) and pharmaceuticals and personal care products (PPCPs) from urban sewage. MTF and ASP resulted in >1 log unit reduction in the abundance of ARB, while for ARGs, the removal was observed in the range of 0.1 to 1.7 log units. In MTF, ARGs were substantially removed in the aerobic zone compared to the anoxic zone. The relative abundance of most of the ARGs either decreased or remained unchanged during MTF and ASP operations. However, the relative abundance of most of the ARGs increased in the secondary sludge generated from ASP. The concentration of PPCPs such as atenolol, sulfamethazine, triclosan, and ranitidine was reduced by MTF by >80 %. Overall, the results indicated that MTF followed by ozonation is the most effective combination for removing emerging contaminants from municipal sewage.

Cultivation of microalgal-bacterial granular sludge from activated sludge via granule inoculation: Performance and microbial community

This research devoted to cultivate microalgal-bacterial granular sludge (MBGS) from activated sludge by inoculation with mature MBGS. It was found that the inoculation helped to the successful cultivation of MBGS from activated sludge within 25 days. The newly established MBGS system could stably achieve considerable organics, ammonia and phosphorus removals. Extracellular polysaccharides and aromatic proteins might contribute to the MBGS formation and growth. In addition, the inoculation led to functional microbial communities of MBGS for stable pollutants removal. Specifically, the abundance of phosphorus accumulating organisms rose significantly including Leptolyngbyaceae and Comamonadaceae. Based on the above findings, the possible process of MBGS cultivation from activated sludge by inoculation was depicted. This research would offer insight into the establishment of next-generation wastewater treatment process of MBGS from the conventional activated sludge process in future.

Studying the Effects of Organic and Hydraulic Shock Loads on the Membrane Bioreactor (MBR) By Using GPS-X Mathematical Model

Membrane-based systems (MBR) used in wastewater treatment have many advantages over conventional activated sludge processes. They have proven to be very effective in removing organic and inorganic contaminants as well as biological entities from water. The objective of this work is to propose an optimal operation of the bioreactor after having detailed in the relationships between the nature of the sludge, its conditions is obtaining the performance of the membrane using a simulation software (GPS-X). The effects of organic and hydraulic shock loads on the MBR system were also studied. The GPS-X simulation program was used in this study to simulate the membrane bioreactor setup. The BOD removal system we used was 78%. In addition, the MBR system has a significant capacity due to the hydraulic shock load of the operation and the process efficiency for the MBR installation due to this shock load based on BOD removal was reduced up to 65%. The MBR system has a good ability to handle the organic shock loads of the operation with no significant loss in treatment efficiency. The treatment efficiency of the MBR system, due to organic shock loads based on BOD removal, decreased slightly to 80%, however, it is shown how their properties determine the extent of sludge fouling in the membrane. Based on these results, operational conditions favoring a reduction of fouling are proposed.

Sludge retention time effects on recovery of soluble organic matters via polyhydroxyalkanoate storage in contact stabilization process under feast/famine regime

AbstractBACKGROUNDContact stabilization (CS) can be used to capture organic matters from wastewater. However, CS is less efficient in capturing soluble organic matters (SOMs). Recovery of SOMs is required to minimize carbon emission and to maximize organic recovery from wastewater.RESULTSSOMs were recovered by applying a feast/famine (F/F) regime in a CS process. Sludge retention time (SRT) was found to regulate the recovery efficiency of SOMs. At a SRT of 4 d, 44.7% of the removed soluble chemical oxygen demand (SCOD) in wastewater was recovered and stored into intracellular polyhydroxyalkanoates (PHA), leading to 12.8% decrease of CO2 emission in comparison with the conventional activated sludge process. The storage of PHA in waste sludge harvested at a SRT of 4 d significantly increased the methane yield (187.3 ± 5.9 mL (g VSS)−1). The dominant bacteria performing SOM recovery in CS belonged to the genera Tessaracoccus, norank_f__Caldilineaceacea, unclassified_f__Microbacteriaceae and Flavobacterium.CONCLUSIONSThe study demonstrated that applying F/F regime in a CS process can recover SOMs via PHA storage. The regulation of SRT can enhance SCOD recovery. The study provides a solution to enhance SOM recovery from wastewater instead of being oxidized into CO2. © 2022 Society of Chemical Industry (SCI).Highlights SCOD can be recovered via PHA by applying F/F regime in CS mode. The optimum SRT of 4 d resulted 44.7% SCOD recovery via PHA storage. PHA‐accumulating bacteria belonged to four genera. Anaerobic digestion of sludge resulted in a 17.6% higher CH4 yield. CO2 emission decreased 12.8% compared with conventional activated sludge process.

Performance evaluation and microbial community structure of a modified trickling filter and conventional activated sludge process in treating urban sewage

This study compares the performance and microbial composition of a conventional activated sludge process (ASP) with a modified trickling filter (MTF) for urban sewage treatment. MTF (2 h HRT with effluent recycling) and ASP (8 h HRT) showed >60 % removal efficiency for COD, NH3-N and PO43−-P. MTF outperformed ASP in denitrification and 5 mg/L of NO3−-N was detected in the effluent of MTF. The widespread distribution of nitrogen removal functional genes (amoA, nirK, nirS, napA, narG and nosZ) in MTF indicates simultaneous nitrification and denitrification (SND) as a key process controlling nitrogen removal. In addition, Miseq sequencing was used to examine the microbial community composition in MTF and ASP. The sequencing result revealed that Proteobacteria, Planctomycetes, Chloroflexi and Actinobacteriota were the dominant phyla in both MTF and ASP. Moreover, the co-occurrence of various nitrifiers, denitrifiers, aerobic denitrifiers, and ANAMMOX bacteria in MTF suggested their role in nitrogen removal.

Removal performance of SARS-CoV-2 in wastewater treatment by membrane bioreactor, anaerobic-anoxic-oxic, and conventional activated sludge processes

The potential risk of SARS-CoV-2 in treated effluent from a wastewater treatment plant (WWTP) is concerned since SARS-CoV-2 is contained in wastewater during the COVID-19 outbreak. However, the removal of SARS-CoV-2 in WWTP has not been well investigated. The objectives of this study were (i) to clarify the removal performance of SARS-CoV-2 during wastewater treatment, (ii) to compare the removal performance of different secondary treatment processes, and (iii) to evaluate applicability of pepper mild mottle of virus (PMMoV) as a performance indicator for the reduction of SARS-CoV-2 RNA in wastewater treatment. Influent wastewater, secondary-treatment effluent (before chlorination), and final effluent (after chlorination) samples were collected from a WWTP from May 28 to September 24, 2020, during the COVID-19 outbreak in Japan. The target WWTP had three parallel treatment systems employing conventional activated sludge (CAS), anaerobic-anoxic -oxic (A2O), and membrane bioreactor (MBR) processes. SARS-CoV-2 in both the liquid and solid fractions of the influent wastewater was concentrated and quantified using RT-qPCR. SARS-CoV-2 in treated effluent was concentrated from 10 L samples to achieve a detection limit as low as 10 copies/L. The log reduction value (LRV) of SARS-CoV-2 was 2.7 ± 0.86 log10 in CAS, 1.6 ± 0.50 log10 in A2O, and 3.6 ± 0.62 log10 in MBR. The lowest LRV observed during the sampling period was 2.8 log10 in MBR, 1.2 log10 in CAS, and 1.0 log10 in A2O process, indicating that the MBR had the most stable reduction performance. PMMoV was found to be a good indicator virus to evaluate reduction performance of SARS-CoV-2 independent of the process configuration because the LRV of PMMoV was significantly lower than that of SARS-CoV-2 in the CAS, A2O and MBR processes.

Impact of seed sludge characteristics on granulation and performance of aerobic granular sludge process

Characteristics of seed sludge are of great importance in granulation and treatment performance of aerobic granular sludge process. Fast-settling floccular sludge has been shown to be affective on accelerating granulation. High-rate activated sludge process provides organic matter capturing from municipal wastewaters in order to harvest the chemical energy through adsorption rather than mineralization. Thus, waste sludge from the high-rate activated sludge process settles fast since the biosorption is the main mechanism in this technology. In this paper, impact of different seed sludge characteristics on granulation, and treatment performance of an aerobic granular sludge system was comparatively evaluated by seeding the system with solely conventional waste activated sludge (Stage 1) and a mixture of waste sludge from a conventional activated sludge process and a high-rate activated sludge process (Stage 2). Although the aerobic granular sludge reactor was seeded with a sludge that had a higher median particle size at Stage 2, after steady state conditions have been reached during the operation, average median particle size in the reactor at Stage 1 (124 ± 2.8 μm) was higher than that at Stage 2 (86 ± 2.7 μm). High ammonium nitrogen removal efficiencies (>98%) obtained in the study, however, total nitrogen (TN) and total phosphorus (TP) removal efficiencies obtained at Stage 2 (TN: 66.7 ± 2.2%; TP: 13.2 ± 2.9%) were lower those at Stage 1 (TN: 80.9 ± 2.2%; TP: 92.7 ± 4.4%). One of the reasons of incomplete denitrification and decreased phosphorus removal efficiencies observed at Stage 2 was smaller granules that was the cause of less anoxic/anaerobic volume. Another possible reason was the absence of denitrifiers, and polyphosphate-accumulating organisms in the high-rate activated sludge. Although high efficiencies were achieved in COD and ammonia removal by aerobic granular sludge process seeded with different types of sludge, this study showed that seed sludge affected anoxic/anaerobic volumes in the granules and thus affected denitrification and phosphate accumulation. Nitrogen and phosphorus loads resulting from wastewater treatment plants must be controlled and decreased before their discharge into the receiving water bodies. From this perspective, this study highlights the importance of seed sludge type on nitrogen and phosphorus removal performance of aerobic granular sludge process.

Occurrence and removal of organophosphate esters in municipal wastewater treatment plants in Thessaloniki, Greece

An integrate study regarding the occurrence and fate of eleven organophosphate esters (OPEs) was conducted at two wastewater treatment plants (WWTPs) in the area of Thessaloniki, Greece. Both plants employed conventional activated sludge process whereas as last treatment step the first unit use chlorination and the second one ozonation. OPEs were determined in dissolved fraction, total suspended solids and sludge from various treatment stages of WWTPs. Tris (2-butoxyethyl) phosphate (TBOEP), tris (1-chloro-2-propyl) phosphate (TClPP) and triphenylphosphine oxide (TPPO) were the most abundant compounds in influent and treated effluent. Triphenyl phosphate (TPHP) was also abundant in suspended solids and sludge. Total concentrations of ∑11OPEs ranged from 2144 to 9743 ng L−1 in influents, 1237–2909 ng L−1 in effluents and 3332–14294 ng g−1 dw in sludge. Removal rates from 55% to 80% were observed for most OPEs, whereas chlorinated OPEs, especially for tris(2-chloroethyl) phosphate (TCEP) exhibited low removal efficiency. Mass balance analysis showed that biodegradation was the dominant removal mechanism contributing up to 85%. Sorption onto sludge was also relevant removal pathway for most compounds. Emissions of OPEs through effluents and sludge did not pose considerable risk to the aquatic and terrestrial environment.

Carbon-neutral treatment of N, N-dimethylformamide-containing industrial wastewater by anaerobic membrane bioreactor (AnMBR): Bio-energy recovery and CO2 emission reduction

High-strength industrial wastewater containing approximately 2000 mg/L of N, N-dimethylformamide (DMF) was treated by the anaerobic membrane bioreactor (AnMBR) during a long-term operation with the concept of carbon neutrality in this study. Bio-methane was recovered as bio-energy or bio-resource from DMF-containing wastewater along with the CO2 emission reduction. The results are clear evidence of the feasibility of carbon–neutral treatment of DMF-containing wastewater by the AnMBR. With an effective degradation under the organic loading rate of 6.53 COD kg/m3/d at the HRT of 12 h, the AnMBR completely covered the energy consumption during long-term operation by saving electricity of 4.16 kWh/m3 compared with the conventional activated sludge process. The CO2 emission of the AnMBR was just 1.06 kg/m3, remarkably reducing 1.45 kg/m3 of CO2. The treatment of DMF-containing wastewater by the AnMBR perfectly realized the goal of carbon neutrality, and was considered as an alternative to the conventional activated sludge process.

Integrating electrochemical pretreatment (EPT) and side-stream sulfidogenesis with conventional activated sludge process: Performance, microbial community and sludge reduction mechanisms

• Coupling EPT and sulfidogenic side-stream reactor (ESSR) with CAS process was studied. • EPT at 15 V/5min with 125 mg S/L of SO 4 2− dosage improved sludge reduction. • The ESSR could be designed with a very short SRT of 2.5 days. • The integrated process (ESSR-CAS) was operated over 200 d with good performance. • Possible reasons for fast sludge hydrolysis in ESSR-CAS were discussed. Recently, inserting an anaerobic side-stream reactor into a conventional activated sludge (CAS) process for upgrading biological wastewater treatment plants with in-situ sludge reduction function has been extensively studied. A typical example is an oxic-settling anaerobic (OSA) process, which can achieve efficient sludge reduction, but requires ample space, limiting its application potential. Optimizing the conventional OSA process towards compact and energy-efficient is necessary. This paper studied a new method by integrating electrochemical pretreatment (EPT) and sulfidogenesis-enhanced anaerobic treatment with a conventional OSA process to achieve considerable in-situ sludge reduction with a limited side-stream size requirement (i.e. short sludge retention time (SRT)). The proposed idea was verified experimentally – first, batch experiments were conducted to determine the effective sulfate concentration for the EPT and sulfidogenic side-stream reactor (ESSR); then, the ESSR-CAS process (upgrading CAS with a new ESSR) and a stand-alone CAS process (control) were operated in parallel for 200 days. The experimental results showed that: The new ESSR, with approximately 125 mg S/L of sulfate dosed and 5 min electrochemical sludge pretreatment at 15 V, can successfully accelerate anaerobic reactions, resulting in a short SRT of 2.5 days. The ESSR-CAS process can reduce sludge production by 61%, with high soluble chemical oxygen demand (SCOD) and total nitrogen (TN) removal efficiencies of 96% and 70% respectively. The possible mechanisms of ESSR for the augment of sludge hydrolysis (sludge floc disintegration, extracellular polymer destruction, and cell structure breakage) as well as the economic considerations of this new sulfur-cycle bioprocess are discussed.

Applying novel methods in conventional activated sludge plants to treat low-strength wastewater

Conventional activated sludge system is confidently widely used for biological treatment plants of municipal wastewater but suffering from operation problems that affect their efficiencies and effluent qualities, especially when treating low-strength wastewater with increasing incoming flow. The objective of this study is to evaluate and compare the novel methods used in upgrading conventional activated sludge treatment systems receiving low-strength wastewater to generate good effluent quality. GPS-X Simulator V 8.0 was used for model calibration and plant performance prediction. The calibrated GPS-X model proved that eliminating primary settling from the treatment process does not affect BOD5 and COD removal, while TSS removal is decreased, and NH4-N removal is increased. Increasing the return activated sludge flow from 50 to 150% of influent flow does not affect conventional activated sludge process, while the change of waste activated flow had a vital effect on process performance. The presence of an anoxic zone in conventional activated sludge processes treating low-strength wastewater has no significant impact on plant performance. Also, the model outputs proved that adding filling media to the aeration tank was able to handle an increase of influent flow and a stable performance of BOD5, and NH4-N removal was observed.

Effect of short-term light irradiation with varying energy densities on the activities of nitrifiers in wastewater

Microalgal-bacterial consortium (MBC) process has been proposed as an alternative to conventional activated sludge process for nitrogen removal from wastewater. As one of the most influencing parameters, light irradiation effects on microalgae have been extensively investigated. However, light influence on the performance of nitrifiers in activated sludge and its mechanism remains unclear. In this study, the effects of three factors (light irradiation power, irradiation time and sludge concentration) on activities and physiological characteristics of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were systematically studied through both the Design of Experiments driven response surface methodology (RSM) approach and light-nitrification kinetic modeling. Results indicated that light irradiation with the specific light energy density (Es) at 0.0203–0.1571 kJ·mg−1 VSS (80–160 W/400–1000 μmol·m−2·s−1, 2.0–5.0 h and 2750–4250 mg·L−1) stimulated the relative AOB activities (rAOB) by 120.0%. This was supported by the increased electron transport system activity, key enzyme activity (AMO) , gene expression (amoA) and energy generation (ATP consumption) in the light treatment. Moreover, further Es increasing up to 0.18 kJ·mg−1 VSS inhibited both AOB and NOB activities. The inhibition was ascribed to the joint light responses of metabolic disorders and lipid peroxidation. The findings enhance our understanding of nitrifiers’ physiological responses to short-term light irradiation, and promote the development of MBC as a sustainable approach for wastewater treatment.

The effect of zero-valent iron/Fe3+ coupling and reuse on the properties of anoxic sludge

Mud-water separation efficiency and removal efficiencies of pollutants are relatively low in conventional activated sludge processes. In this study, zero-valent iron (ZVI) and Fe3+ were added into an activated sludge system and combined to improve sludge flocculation and effluent quality in an anoxic zone. The effects of ZVI/Fe3+ on removal efficiencies of nitrogen and phosphorus were investigated and the contact angle, Zeta potential and particle size of the sludge were analyzed. Changes in the ZVI crystal structure, element valence and corrosion rate were also explored. The results suggest that the addition of ZVI improved the removal efficiencies of chemical oxygen demand (COD) and total phosphorus (TP) by enhancing the electron transfer rate. Removal efficiencies of COD and TP were highest (72.66% and 98.66%, respectively) following the addition of 10 g/L of ZVI and 10 mg/L of Fe3+. Nitrate nitrogen (NO3−-N) was removed by ZVI/Fe3+ under biological and chemical action and its removal efficiency was directly proportional to ZVI content. Sludge flocculation after the addition of Fe3+ alone was better than that after the addition of ZVI alone. The combined action of ZVI/Fe3+ significantly increased particle size, Zeta potential and hydrophilicity of the sludge. Electron transfer was accelerated by the addition of 30 g/L of ZVI and 10 mg/L of Fe3+. More than 90% of the ZVI could be recovered, although flake and needle-like corrosion products existed on the surface of the recovered ZVI. The specific surface area of recovered ZVI increased and it could still effectively remove pollutants even when reused three times.

Treatment of vegetable oil wastewater by a conventional activated sludge process coupled with electrocoagulation process.

The present work aims to study chemical oxygen demand (COD), oil-grease, and color removal from vegetable oil wastewater by combined electrocoagulation and activated sludge processes. For this purpose, the sample was pretreated using electrocoagulation by various optimization parameters such as electrode type (Al-Al and Fe-Fe), current density (100-400 A/m2 ), pH (2-8), and electrolysis time (15-180 min). The results showed that 89.3% of COD, 100% of oil-grease, and 66.2% of color were removed by electrocoagulation under the conditions of 300-A/m2 current density, pH 2, and 180-min reaction time with Al-Al electrode pairs. Then, the effluent of electrocoagulation was treated by an activated sludge process. The results depicted that the activated sludge process was also effective for vegetable oil wastewater treatment and it enhanced 98.9% COD and 79.2% color removal efficiency. The effluent of the combined process was very clear, and its quality exceeded the direct discharge standard of the water pollution control regulation. The laboratory-scale test results indicate that the combined electrocoagulation and activated sludge process is feasible for the treatment of vegetable oil wastewater. PRACTITIONER POINTS: Vegetable oil wastewater was treated by combination of electrocoagulation and activated sludge processes. The combined electrocoagulation and activated sludge processes supplied 99.9% COD, 100% oil-grease, and 93.0% color removal efficiency. The laboratory-scale test results indicate that the combined EC-SBR processes were feasible for the treatment of vegetable oil wastewater.

Removal Performance of SARS-CoV-2 in Wastewater Treatment by Membrane Bioreactor, Anaerobic-Anoxic-Oxic, and Conventional Activated Sludge Processes

Removal Performance of SARS-CoV-2 in Wastewater Treatment by Membrane Bioreactor, Anaerobic-Anoxic-Oxic, and Conventional Activated Sludge Processes

Sustainable design of textile industry effluent treatment plant with constructed wetland

Textile has become a major source of income for India’s economy. Steps involved in textile manufacturing are fabrication of yarn, fabric production, dying, printing and finishing. Dying, printing and finishing are mainly water intensive processes which results in the generation of liquid waste. This effluent contains essential compounds such as salts, acids, alkalis and anthropogenic dyes in good concentration Many times dyes acts as sources of heavy metals also. Effluent from this type of industries not only makes the water body unfit for downstream use but also disturbs the natural aquatic ecosystems. Coloured textile effluent after joining any water body make the water unfit for downstream usage as well as interfere with natural activities of aquatic life. Developing countries thus require effective, economic and environment friendly sustainable treatment option.Constructed Wetlands (CW) provide an economic, easy as well as environment friendly treatment option having the ability to treat even different industrial effluents. CW has been found to be 42 %more economical than activated sludge process where as 80% more economical based on operation and maintenance expenses. In the current study, effort has been given to design a sustainable textile industry effluent treatment plant with Constructed Wetland. CW has been designed by various methods, under different flow conditions and indifferent weather conditions. The site under study had a green belt of 1500 sq. meter. According to k-C* model while considering the chemical oxygen demand (COD) load both horizontal as well as vertical subsurface flow, CW can be constructed in these green belt. As a result of current study, it was concluded that CWs are capable enough to replace the conventional activated sludge process (ASP). CW design has been done on the basis of both biological oxygen demand (BOD) as well as COD load for summer and winter conditions. K-C* model gave reliable result. The organization under study is having a green belt of 1500 sq. mts. According to k-C* model the horizontal CW can be designed after giving pre-treatment by ASP where for vertical subsurface flow CW the treatment can be more sustainable and the effluent can be wholely treated by CW.

Direct visualization of hollow fiber membrane fouling distribution

Submerged membrane bioreactor system is commonly used for water and wastewater treatment processes. This system is a more economical alternative to conventional activated sludge process due to small footprint and better effluent quality. Nevertheless, membrane fouling is a major issue that requires further studies. This paper covers the use of an optical microscope to observe membrane fouling. Bentonite was used as model particles to simulate activated sludge. In-situ observation of particle deposition along the surface of hollow fiber membranes during filtration was performed at various operating conditions. Results from this studies indicated that the flux distribution was affected by the permeate flux and cross flow velocity. Lower CFV and higher flux caused the flux to be more non-uniformly distributed due to more severe fouling. These findings provided useful information to further improve the membrane module design to achieve more evenly distributed permeate flux.

Removal of Emerging Contaminants from Wastewater Streams Using Membrane Bioreactors: A Review.

Water is a very valuable natural resource. As the demand for water increases the presence of emerging contaminants in wastewater has become a growing concern. This is particularly true when one considers direct reuse of wastewater. Obtaining sufficient removal of emerging contaminants will require determining the level of removal for the various unit operations in the wastewater treatment process. Membrane bioreactors are attractive as they combine an activated sludge process with a membrane separation step. They are frequently used in a wastewater treatment process and can operate at higher solid loadings than conventional activated sludge processes. Determining the level of removal of emerging contaminants in the membrane bioreactor step is, therefore, of great interest. Removal of emerging contaminants could be by adsorption onto the biomass or membrane surface, biotransformation, size exclusion by the membrane, or volatilization. Given the fact that most emerging contaminants are low molecule weight non-volatile compounds, the latter two methods of removal are usually unimportant. However, biotransformation and adsorption onto the biomass are important mechanisms of removal. It will be important to determine if the microorganisms present at given treatment facility are able to remove ECs present in the wastewater.

A Review on Internal Design Modifications in Activated Sludge Process: Status, Impact and Recommendations

With water crisis getting severe each year all over the world, development in waste water recycling techniques has gained momentum to meet strict environmental norms and to take advantage of the recyclability of water. Biological treatment methods predominate over other recycling methods as they are less expensive and do not generate secondary pollutants. Challenges faced in using these methods such as low oxygen solubility in water or insufficiency in maintaining booming environment for microorganisms and sludge water separation issues restrain their full fledge utilization, thus hampering expenditure control and the final effluent quality which can be achieved otherwise. The developments made so far to overcome drawbacks of conventional activated sludge process revolves around modifications in suspended, attached growth process and improvements via integration of both systems. Further process refinement includes modifications in aeration and sludge separation systems but lacks the cost analysis for scale up. This paper critically reviews various internal design modifications made in aerobic treatment of wastewater by several researchers on lab and pilot scale to overcome the problem faced while operation. This paper also gives guidelines to meet the design objectives for a commercial scale wastewater treatment plant from process efficiency and economy aspects.

Reduction of Cost and Environmental Impact in the Treatment of Textile Wastewater Using a Combined MBBR-MBR System.

A hybrid Moving Bed Biofilm Reactor—Membrane Bioreactor (MBBR-MBR) was developed for the treatment of wastewater from a Spanish textile company. Compared with conventional activated sludge (CAS) treatment, the feasibility of this hybrid system to reduce economic and environmental impact on an industrial scale was conducted. The results showed that, technically, the removal efficiency of COD, TSS and color reached 93%, 99% and 85%, respectively. The newly dyed fabrics performed with the treated wastewater were qualified under the standards of the textile industry. Economically, the values of Capital Expenditure (CAPEX) calculated for the hybrid MBBR-MBR system are profitable because of the reduction in Operational Expenditure (OPEX) when compared with CAS treatment, due to the lower effluent discharge tax thanks to the higher quality of the effluent and the decolorizing agent saved. The result of Net Present Value (NPV) and the Internal Rate of Return (IRR) of 18% suggested that MBBR-MBR is financially applicable for implantation into the industrial scale. The MBBR-MBR treatment also showed lower environmental impacts than the CAS process in the life cycle assessment (LCA) study, especially in the category of climate change, thanks to the avoidance of using extra decolorizing agent, a synthetic product based on a triamine.