Primary Tank Research Articles

Differences in the isotopic signature of activated sludge in four types of advanced treatment processes at a municipal wastewater treatment plant

The natural abundance of stable isotopes is a powerful tool for evaluating biological reactions and process conditions. However, there are few stable isotope studies on the wastewater treatment process. This study carried out the first investigation on variations in natural abundance of carbon and nitrogen stable isotope ratios (δ13C and δ15N) of activated sludge in four types of advanced treatment process (extended aeration activated sludge (EAAS), aerobic-anoxic-aerobic (A2O), recycled nitrification-denitrification (RND), and modified Bardenpho (MB)) at a municipal wastewater treatment plant. The δ13C and δ15N values of influent suspended solids settled in the primary sedimentation tank (i.e., primary sludge) ranged from −25.4‰ to −24.6‰ and 0.5‰–2.9‰, respectively, during monitoring periods. The δ13C values of the activated sludge were −24.6‰ to −23.6‰ (EAAS), −25.4‰ to −24.3‰ (A2O), −25.7‰ to −24.9‰ (RND), and −25.7‰ to −24.3‰ (MB). The δ13C values of the activated sludge were similar to those of influent suspended solids. However, the δ13C values of activated sludge in EAAS was significantly higher than in A2O, RND, and MB. Meanwhile, the δ15N values of activated sludge were obviously higher than influent suspended solids; 5.8‰–7.5‰ (EAAS), 6.6‰–8.1‰ (A2O), 5.5‰–7.5‰ (RND), and 5.3‰–7.6‰ (MB). Changes in δ13C and δ15N values of the activated sludge within the treatment system were also found. These findings indicate that changes in δ13C and δ15N values of the activated sludge rely on important function for biological wastewater treatment such as nitrification, denitrification, and methane oxidation through wastewater treatment over time.

Technology for biological treatment of urban wastewater and sludge treatment with deep removal of nitrogen and phosphorus

This article is dedicated to increasing of removing of nitrogen and phosphorus in DENIFO technology, and the removing of phosphorus by reagents. Removal of nitrogen and phosphorus from municipal wastewater prevents eutrophication of open water, which has become a global problem. A list of conditions that provide maximum efficiency of the processes of wastewater treatment and sludge treatment is completed. Functions of primary settlers, air tanks (based on technology DENIFO), and secondary settlers is reviewed. Pre-denitrification of the returned active sludge with the partial flow of waste water improves anaerobiosis in the anaerobic zone of biological block, and promotes intensive dephosphorization. The work was made under normal conditions of wastewater treatment plant. Unfavorable periods (snowmelt, torrential rains, floods) are not taken into consideration. Mathematical equations are made for the average flow of wastewater during dry weather. Combined dehydratation of the sludge and sediments (the long stay in the tank) leads to rapid displacement phosphorus phosphate to drain water, and a corresponded increase the content of phosphorus in the treated water. Also recommendations for changing the operating mode of the block of sludge treatment given. The important results included in article was taken on the really functioned wastewater treatment plants of Saint Petersburg. This work is aimed at a comprehensive assessment, development and improvement of technology of removing nitrogen and phosphorus from municipal wastewater, including from secondary pollution coming from the return flow from the sludge treatment units.

Investigation of effective factors on the ammonia removal efficiency in the wastewater treatment plants using the air stripping process

Removal of ammonia from wastewater in the wastewater treatment plants due to its dangerous and toxic effects on human health and biotic resources is essential. This study was aimed to investigate the effective operational parameters on the efficiency of the air stripping process, determine their priority and degree of effect on ammonia removal and compare the ammonia removal efficiency during the air stripping process in the municipal treatment plants using synthetic and real wastewater.In this study, the effect of each operating parameter on the ammonia removal efficiency including initial ammonia concentration, pH and temperature during the air stripping process for synthetic and real wastewater, respectively, based on standard methods (the Nesslerization method, preparation of standard solutions) using a spectrophotometer, pH meter and temperature module were evaluated.The results of this study showed that the maximum of ARE for synthetic wastewater with Air to water ratio 80 and an initial ammonia concentration of 59. 6 mg /l, pH 12.05 and temperature 46.3°C was %91. Also, the results of the study on the ARE during the air stripping process showed that the maximum of ARE (%91) for real wastewater (primary sedimentation tank effluent (PST)) with Air to water ratio 80 and an initial ammonia concentration of 61.04 mg/l, pH 12.53 and temperature 45.9 ° C was obtained.Based on the results of univariate regression model, initial ammonia concentration˃ temperature˃ pH have the greatest effect on the ammonia removal efficiency in synthetic wastewater and real wastewater, respectively. In the multivariate regression model, the effect of temperature and pH on the ammonia removal efficiency in synthetic and real wastewater is increasing and decreasing, respectively. Based on the findings of this study, the air stripping process can be successfully used to remove ammonia from wastewater in the municipal treatment plants, especially in the tropics.

Feeding preparation strategy for the supercritical water oxidation (SCWO) system for disposing of liquid hazardous waste

Abstract Supercritical water oxidation (SCWO) technology has a great potential application for the disposal of liquid hazardous wastes. The feeding process is vital for the safety and normal operation of SCWO. This paper describes the feeding preparation strategy of SCWO with multilevel grouping and programming. Based on the physicochemical properties, the liquid hazardous wastes from various industrial manufacturers were first grouped into acid, neutral and alkaline groups. By mixing between samples, the primary grouping tanks were determined to be acid, alkali, amphoteric reacting, organic and organic high-chlorine liquid wastes. By distributing acid, alkali, amphoteric reacting liquid wastes into organic wastes, three parallel feeding routes are regulated for the homogenizing tank phase, which avoids the reaction between wastes. By calculating with the linear programming optimization model of MATLAB, the waste compatibility ratio of each feeding route was determined to meet the feeding requirements of SCWO. The feeding preparation strategy of this paper provides a practical instruction for the SCWO design and operation.

The development of a calibration methodology for a realistic primary settling tank (PST) model

The previous models that replicated primary sedimentation units assumed that all the total settleable solids (TSS) components settled at the same velocities. These assumptions resulted in poor predictions of primary sludge characteristics and anaerobic digestion (AD) model. With the accurate knowledge of PS compositions, the settled wastewater that leads to the activated sludge (AS) system can be determined using the principles of material mass balance. The mass balance is achieved by consolidating the known compositions of raw wastewater and primary sludge (PS) hereby allow accurate tracking of elements along the entire WRRF when using the model for design and optimised operation of WRRF systems. In this investigation, the raw wastewater entering the water and resource recovery facility (WRRF) via the PST is comprehensively characterising the TSS. The TSS was categorised into inorganic settleable solids (ISS), biodegradable particulate organics (BPO) and unbiodegradable particulate organics (UPO), each with five settling velocity distribution profiles. The BPO is further defined in terms of its elemental composition and hydrolysis rate kinetic constants to allow for accurate prediction of the AD system performance when linked to the virtual PST. To achieve this, the study introduced the (i) modification of the University of Cape Town Primary Sedimentation Unit (UCTPSU) model of (Polorigni et al., 2021), by the inclusion of hydrolysis and acid fermentation bioprocesses, and (ii) calibration of the UCTPSU model. The calibration was conducted through the (a) performance of a sensitivity analysis on the modified UCTPSU model and (b) the utilisation of the data generated from settleometer and augmented bio-methane potential (ABMP) tests.

Occurrence and fate of androgens, progestogens and glucocorticoids in two swine farms with integrated wastewater treatment systems

Steroid hormones are endocrine-disrupting chemicals that can cause adverse effects even at trace levels. The information about steroid hormones in animal wastes is still very limited. Here we investigated the occurrence and fate of fourteen androgens, twenty-one progestogens, and five glucocorticoids in Farm Luo Cheng (LC) and Farm Shui Tai (ST) with integrated wastewater treatment systems (WTSs) in South China. These two integrated systems have four stages: primary treatment (primary sedimentation tank), secondary biological treatment (biogas digester and up-flow anaerobic sludge reaction bed (UASB)), third-stage disinfection process, and fourth-stage dilution and further biodegradation process (oxidation fish ponds/lagoons). A total of 31 target steroid hormones were detected in the wastewater of the two swine farms, with concentrations ranging from 0.12 ng/L (medroxyprogesterone acetate, MPA) to 11,200 ng/L (5α-dihydroprogesterone, 5α-DHP). A total of 22 target steroid hormones were detected in feces, of which 19 were detected in Farm LC and 17 in Farm ST. Some of these detected steroids were synthetic chemicals, which might be parent chemicals from exogenous addition or their metabolites, or transformation products from other natural steroids. The steroids excretion of sows in swine farms were estimated, with some steroids such as androstenedione (AED, 41.5 μg/d), epiandrosterone (EADR, 268 μg/d), progesterone (P, 661 μg/d), and 5α-DHP (982μg/d) having much higher values than those from human bodies. Both WTSs in the swine farms could effectively remove the target steroid hormones, with the removal rates of most targets exceeding 90%. In comparison, the anaerobic digester-A2/O (anaerobic-anoxic-oxic)-lagoon system performed better in removing steroids than the up-flow anaerobic sludge reaction bed (UASB)-two-stage series (A/O)2-oxidation fish ponds system. However, there were still 22 steroid hormones, including 14 synthetic ones detected in the effluent, with the risk quotients of most synthetic steroids exceeding 1, showing high risks to aquatic organisms. The findings from this study showed that there is a wide presence of steroid hormones, especially some synthetic steroids in animal wastes, posing potential ecological risks, and these steroids should be removed before discharge to the environment.

Plombotectonique des gisements du Maroc

La synthèse de 240 analyses isotopiques du plomb, mesurées sur les gisements miniers marocains d’âges édiacarien à néogène appartenant à tous les domaines géotectoniques du Maroc autorise une réflexion globale sur la métallogénie du Maroc. Les compositions isotopiques varient grandement, de 17,738 (Bou Skour) à 18,905 (Draa Sfar) pour le rapport 206Pb/204Pb, et de 15,521 à 15,706 pour le rapport 207Pb/204Pb. La source du plomb des gisements étudiés se situe dans la croûte continentale supérieure, excepté pour ceux de l’Anti-Atlas (Bou Skour, Imiter…) et certains du Haut-Atlas (Azegour) à nette contribution du manteau. Les variations isotopiques relevées à l’échelle d’un district résultent soit de la présence de plusieurs événements hydrothermaux superposés sollicitant différentes sources locales comme à Tighza, soit d’un seul événement perturbé par la segmentation d’un bassin volcanosédimentaire, comme pour les amas sulfurés des Jebilet et Guemassa. À l’échelle du gisement (Draa Sfar, Bou Skour), les variations isotopiques résultent de la superposition de plusieurs événements hydrothermaux avec chacun leur propre plomb et métaux associés. Globalement, on peut distinguer trois générations de plomb incorporées successivement dans le socle géologique marocain par le magmatisme et/ou l’hydrothermalisme, caractérisées par leurs rapports 206Pb/204Pb : 17,74–17,90 (panafricain), 18,10–18,40 (hercynien) et 18,75–18,90 (alpin). Le plomb panafricain est présent dans l’Anti-Atlas, et très localement dans la Meseta (Bouznika), et se nourrit en partie du magmatisme mafique du Gondwana. Le plomb hercynien est le plus représenté et affiche une rupture définitive dans la source des métaux dès lors exclusivement crustale. Il envahit tous les domaines marocains, y compris l’Anti-Atlas, où il remobilise et se mélange avec le plomb panafricain. Le plomb alpin, plus discret, jalonne la large écharpe allant d’Agadir à Nador qui trace en surface le panache mantellique des Canaries et accompagne un magmatisme néogène qui peut aussi avoir agi comme simple moteur remobilisant le plomb hercynien, notamment pour former les gisements MVT de Touissit. Les plombs hercynien et alpin sont en partie responsables du rajeunissement des minéralisations néoprotérozoïques, comme à Bou Azzer ou Imiter. Le Maroc illustre le modèle de Sawkins avec un apport majeur du plomb lors du magmatisme fini-orogénique. Les résultats isotopiques plaident en faveur de remobilisations successives du plomb stocké dans des réservoirs primaires et secondaires avec des phénomènes d’héritage. Enfin le bon transfert de la signature isotopique du plomb des gisements aux gossans de surface, notamment pour les gisements stratiformes de sulfures polymétalliques de type Hajar, montre que la géochimie isotopique du plomb est un outil utilisable pour l’exploration minière au Maroc.

A novel approach to reduce fire-induced domino effect risk by leveraging loading/unloading demands in chemical industrial parks

Due to complexities and uncertainties, risk management of domino effects in chemical plants in operation is challenging. A global optimal risk management scheme can hardly be obtained, therefore, finding a targeted local optimal risk management scheme can be prudent. In the present study, a novel risk management approach is proposed to reduce fire-induced domino effect risk by leveraging loading/unloading demands based on risk aggregation and inventory management. The proposed approach uses the aggregation of three risk indicators as part of the risk management strategy. The first risk indicator is the loss of containment (LOC) risk of chemical installations, which indicates how likely a storage tank may cause a primary fire accident. The second risk indicator is the secondary fire accident inducing ability of chemical installations, which indicates how likely a primary tank may cause secondary fire accidents only. The third risk indicator is the inter-unit closeness degree of chemical installations, which indicates how severe the overall consequence a primary tank may cause. Combining the aggregate risk with the inventory availability of storage tanks, candidate risk management schemes are proposed based on inventory management on chemical loading/unloading demands. The optimal risk management scheme is determined based on the potential losses of fire-induced domino effects. A case study demonstrates the effectiveness of the proposed methodology and risk management strategy for fire-induced domino effects.

Removal of chromium from wastewater using paper waste sludge-derived hyrdrochar modified by naoh

In this work, paper waste sludge (PWS) collected from the primary settling tank of the paper wastewater treatment plant was utilized to generate hydrochar as a low-cost adsorbent for removal of Cr(VI) from aqueous solution. The characteristics of paper waste sludge hydrochar (PWSH) and the effects of adsorption conditions of Cr(VI) onto PWSH, including solution pH (3-9), contact time (5-240 min), initial Cr(VI) concentration (10-80 mg/L) and the adsorbent dose of 1 g/L at room temperature (25±2°C) were investigated. Adsorption isotherm and kinetics were also predicted in this work. The results indicate that the maximum adsorption capacity achieved 11.89 mg/g at 120 min of contact time, pH 3, and initial Cr(VI) concentration of 60 mg/L. The adsorption isotherm was reflected the best by the Langmuir model (R2 of 0.9968). Whereas, the adsorption kinetic also indicates that the pseudo-second-order model predicted the best for Cr(VI) adsorption process with a R2 of 0.9469. The mechanism of Cr(VI) adsorption process onto PWSH was chemical sorption through electrostatic interaction and ion exchange.

Primary sedimentation modelling with characterized setting velocity groups

Within a plantwide water and resource recovery facility context, an important requirement for a primary sedimentation unit model is the correct fractionation of the settleable portion (primary sludge - PS) of the raw wastewater total suspended solids (TSS) according to the (i) unbiodegradable particulate organic (UPO), (ii) biodegradable particulate organic (BPO), and (iii) inorganic settleable solid (ISS) components. This paper focuses on improving a current TSS- based primary settling tank (PST) model to account for correct proportions of these three components, with characterized settling velocity groups.The steps taken towards development of the primary sedimentation unit model involved the development of a discrete particle settling model in Microsoft Excel and the utilisation of well characterised municipal wastewater data from previous studies in the discrete particle settling model, to reproduce PS and settled wastewater outputs in settling fractions of UPO, BPO and ISS, via steady state and dynamic calculations and under strict material mass balances. Finally, the insights obtained from discrete particle settling model calculations were implemented in the development of a dynamic University of Cape Town primary sedimentation unit (UCTPSU) model. This dynamic model was rigorously verified to be internally consistent with regards to material mass balances and utilised to simulate plantwide scenarios, under steady state conditions, whereby the impact of incorrect characterisation of TSS components (UPO, BPO and ISS) fractions was evaluated. From these evaluations, it was noted that the incorrect disaggregation of the TSS components of primary sludge can lead to incorrect predictions with regard to parameters such as the settled wastewater composition and the activated sludge system capacity. Thus, the investigation revealed the need to measure key wastewater parameters such as particle settling velocities and the UPO fraction, towards realistically modelling the primary sedimentation unit operations.

Rainwater harvesting potential assessment for non-potable use in urban areas

Water is an important natural resource which could be utilized for different purposes. Now a day’s water became a scarce resource which needs be conserved. One of the most effective ways to conserve water at urban areas is installing a rainwater harvesting system for the strain of the shower, laundry, plant growth, and construction requirement. This study aimed to determine the rainwater harvesting potential and analyse the importance of a rainwater harvesting system for non-potable use in urban areas. The evaluation of rainwater harvesting was done through surveying and analysis of roof catchment, channel networks, and rainfall data. The assessment of rainwater potential was followed by quantifying the runoff volume and characterization of the rainwater harvesting system components. The investment required for rainwater harvesting within the study site was very small, since it only requires the development primary and secondary sedimentation tanks, and pump cost for lifting the water from the tank to the distribution system. The results of this study indicated that installing a rainwater harvesting system is economical to handle the water scarcity problem within the university. In Debre Tabor University, the available water to be collected from 13 dormitory buildings and also the open area was about 41,511 m3. This revealed that there's an enormous amount of water which is sufficient enough to fulfil the demand for non-potable uses. Hence, the adoption of rainwater harvesting system in urban areas is appropriate method and plays an excellent role in resolving water scarcity problem.

Tracking Robot Location for Non-Destructive Evaluation of Double-Shell Tanks

(1) Background: Non-destructive evaluation of double-shell nuclear-waste storage tanks at the U.S. Department of Energy’s Hanford site requires a robot to navigate a network of air slots in the confined space between primary and secondary tanks. Situational awareness, data collection, and data interpretation require continuous tracking of the robot’s location. (2) Methods: Robot location is continuously monitored using video image analysis for short distances and laser ranging for absolute location. (3) Results: The technique was demonstrated in our laboratory using a mockup of air slot and robot. (4) Conclusions: Location tracking and display provide decision support to inspectors and lay the groundwork for automated data collection.

In Situ Sonification of Anaerobic Digestion: Extended Evaluation of Performance in a Temperate Climate

Increasing the efficiency of anaerobic digesters and improving sludge breakdown is vital to reducing the cost of biogas production and reducing the environmental consequences of sludge disposal. The performance of two unheated anaerobic digestion systems, one exposed to sound at <20 kHz by waterproofed speakers and one acting as a control, were compared for over a year. The digester systems were both composed of primary (11.4 m3) and secondary (3.8 m3) anaerobic tanks, facultative tertiary (3.0 m3) tanks and an aerobic holding tank from which effluent was mixed with feed and recirculated back to the system. Exposure of the gas saturated digestate to a low frequency sine wave induced numerous bubble harmonics up to, and presumably beyond, ultrasonic range, showing that sonification of a highly gaseous liquid might be used to accomplish low power ultrasonication of digestate at greater distances than is possible with conventional ultrasonic technology. Through the summer of 2019, the sound-treated system produced 27% more biogas than the control system, and 74 times more during the winter when biogas production by the control systems essentially ceased. Afterwards, the control system produced more biogas due to depletion of volatile solids in the sound-treated digester. Results show that sound can be used for faster digester startup and substitute for a share of heating requirements during cool months.

Performance evaluation and sustainable, cost-effective and energy-efficient process enhancement measures for Pagla sewage treatment plant, Bangladesh

At present, Pagla Sewage Treatment Plant (STP) is the only sewage treatment plant in Dhaka, the capital city of Bangladesh, with a capacity to treat 120 million litres per day (MLD) of sewage. Evidence suggests that the plant is overburdened and cannot by itself handle the wastewater generated in Dhaka. Furthermore, the treatment plant is hampered by a number of functional problems which limit both its capacity to treat wastewater, and the efficiency of the treatment process. Rectifying the functional problems of the plant and implementing enhancement measures would greatly improve the functionality of Pagla STP. A thorough evaluation was carried out on the performance of the plant and a detailed process flow diagram developed. Several functional problems were identified, mostly pertaining to the primary sedimentation tanks and the unused sludge lagoons. The influent and effluent characteristics of Pagla STP were also assessed using BOD5 values as the primary criteria. It was found that the influent BOD5 value was 832 mg/L and effluent BOD5 was 497.5 mg/L, against design values of 120 mg/L and 50 mg/L respectively. Based on the evaluation, theoretical analysis was done, and a sustainable, cost and energy efficient retrofit was proposed whereby the sludge lagoons would be converted to anaerobic lagoons to facilitate biological pretreatment. It is estimated that implementing such an enhancement would increase the treatment capacity of the plant beyond its original design. Furthermore, theoretical calculations show up to 5,000 m3 of methane gas can be generated daily from the plant, which is enough to power 6,000 homes with renewable energy.

A Novel Check-List Strategy to Evaluate the Potential of Operational Improvements in Wastewater Treatment Plants

With increasing demands for cleaning and purification of water, wastewater treatment plants (WWTP) require their most efficient operation. The operators are thus obliged to constantly review the efficiency of the processing units and technological equipment of WWTPs and seek opportunities for improvements. To increase the efficiency of particular equipment, the important parameters to be used for the intensification must be correctly selected. A common WWTP consists of different types of processing units, where the basic parameters can be changed to achieve the highest efficiency (i.e., maximum output with minimum energy consumption) in the WWTP. However, due to many possible technologies in the wastewater treatment process, the combinations of processing units can be complex. In such cases, the efficiency assessment can be misleading if only basic parameters were accessed. Moreover, single-unit intensification can potentially improve the efficiency of the unit itself but cannot guarantee full process improvement. This can be due to negative causal effects in the downstream due to that unit intensification. This work reviews of key parameters at five selected pieces of WWTP equipment (inlet pump station, airlift pump, primary sedimentation tank, aeration chamber, and mixing of anaerobic digester) to demonstrate the correct selection of all affected parameters for the efficiency assessment. In the context of the whole WWTP process, it is necessary to take into account several other parameters to evaluate the efficiency of the equipment. Finally, a methodology for assessing the significance of the identified parameters is proposed. This methodology is effectively applied and demonstrated in the WWTP case study.

The impact of primary sedimentation on the use of iron-rich drinking water sludge on the urban wastewater system

The impact of primary sedimentation on the multiple use of iron in an urban wastewater system was investigated. Our previous work showed that in-sewer iron-rich drinking water sludge (DWS) dosing exhibited multiple benefits in the downstream processes. However, the system studied did not include a primary settler. We hypothesised that primary sedimentation could significantly change the characteristics of the wastewater flowing to the bioreactor, particularly its particulate components. This could in turn influence the availability of iron for phosphate removal from wastewater and/or sulfide removal in the anaerobic sludge digester. Long-term (~4 months) experiments were carried out on two laboratory-scale wastewater systems, each comprising sewers reactors, a primary sedimentation tank, a wastewater treatment reactor, and an anaerobic sludge digester. It was found the majority (85%) of the Fe contained in the sewer effluent was present in the primary sludge with the remaining (15%) staying in the primary effluent. This significantly affected the flow-on effect of Fe on the phosphate removal during wastewater treatment, removing only 1.2 ± 0.1 mgP L−1, as compared to 3.5 ± 0.1 mgP L−1 achieved previously in the absence of a primary settler. However, the P to Fe removal ratio was 0.32 mgP/mgFe, similar to the ratio observed previously without primary sedimentation (0.36 mgP/mgFe). The dissolved sulfide removal in the anaerobic digester was 2.7 ± 0.5 mgS L−1, substantially lower than 7.2 ± 0.3 mgS L−1 previously attained without primary sedimentation. This suggests that Fe in the primary sludge was not completely available for dissolved sulfide removal in the digester. However, the dewaterability of the anaerobically digested sludge improved with a relative increase of 25.0 ± 0.9%, compared to the 21.7 ± 0.6%, previously observed without primary sedimentation. The results demonstrated that primary sedimentation reduced the effectiveness to deliver the benefits of the in-sewer DWS dosing strategy, but the results are still favourable.

3-Bridge LLC resonant converter for achieving wide output voltage control range based on topology morphing

In this paper, a control method for a 3-bridge LLC resonant converter operating with a wide output voltage control range is described. Duty changes that stem from switching devices cause topology transitions that allow the converter to shift sequentially across four operating modes, where the primary resonant tank circuits and the secondary terminals can be connected in parallel or in series making it possible to achieve a wide controllable output voltage (7.5–120 VDC). During topology mode transitions, morphing control within narrow hysteresis bands, which is achieved by varying the switching frequency and duty of the switching devices, maintains a tight regulation without noticeable output voltage transients. To verify the performance of the proposed converter, a 5-kW 700 VDC input prototype with an output voltage ranging from 7.5 to 120 VDC is built and tested.

Identification of Biogenic Sulphate Corrosion of Concrete in Sewage Treatment Plant Settling Tank Walls

Abstract One of the basic threats in terms of concrete used for tanks or ducts applied in wastewater management is the phenomenon of biogenic sulphate corrosion (BSC). BSC is a particular case of corrosion caused by the action of sulphuric acid (IV), which is formed as a result of a number of biochemical processes, which can take place, e.g. in an environment encountered within the aforementioned structures. Ions present in sulphuric acid react with cement hydration products, which leads to replacing the primary cement matrix components with compounds easily-soluble or highly-swelling during crystallization. The outcome of advanced corrosion is usually an observed formation of a white, amorphous, sponge-like mass, which is easily separated from the underlying concrete. The article discusses a case study of a BSC process in a newly constructed primary settling tank in a municipal wastewater treatment plant.

Factors affecting microplastic retention and emission by a wastewater treatment plant on the southern coast of Caspian Sea

Understanding how wastewater treatment plants (WWTPs) process microplastics (MPs) will help informing management practices to reduce MP emissions to the environment. We show that composite 24 h samples taken at three replications from the outflow of the grit chamber, primary settling tank and clarifier of the WWTP of Sari City, on the southern coast of the Caspian Sea, contained 12667 ± 668, 3514 ± 543 and 423 ± 44.9 MP/m3, respectively. Fibers accounted for 94.9%, 89.9% and 77.5% of the total number of MPs, respectively. The MP removal efficiency was 96.7%. MP shape (fiber, particle), size and structure were the most important factors determining their removal in different steps of the wastewater treatment process. The structure of microfibers (polyester, acrylic and nylon) and the consequent higher density than water explained their high removal (72.3%) in the primary settling tank. However, size was more important in microparticle removal with particles ≥500 μm being removed in the primary settling tank and <500 μm in the clarifier unit. The smallest particles (37–300 μm) showed the lowest removal efficiency. The predominant types of fibers and particles were polyester and polyethylene, respectively, which are likely to originate from the washing of synthetic textiles and from microbeads in toothpaste and cosmetics. Despite the efficiency of the Sari WWTP in removing MPs, it remains a major emission source of MPs to the Caspian Sea due to its high daily discharge load.

Improving primary sludge dewaterability by oxidative conditioning process with ferrous ion-activated peroxymonosulfate

Enhancement of sludge dewaterability is key for sludge management and disposal of wastewater treatment plants (WWTP). In this study, the Fe2+-peroxymonosulfate (PMS) conditioning approach was first used to oxidize the primary sludge from the primary sedimentation tank of a full scale WWTP. The combination of Fe2+ (0.05–0.5 g/g TSS) and PMS (0.05–0.5 g/g TSS) could significantly improve the dewaterability of primary sludge. The optimal addition amount of Fe2+ and PMS was 0.1 g/g TSS and 0.25 g/g TSS, respectively, under which the capillary suction time (CST) and specific resistance to filtration (SRF) of the sludge was reduced by 79% and 95%. The physicochemical properties (particle size, zeta potential, EPS composition) of the primary sludge before and after oxidative conditioning were measured. Results showed that sulfate radicals generated from Fe2+-PMS system effectively reduced organic matter in different EPS fractions, further destroying sludge floc cells. Then the bound water in the sludge flocs was released, thereby improving the sludge dewaterability. The microscopic morphology also indicated that the sludge flocs have a blocky structure with tight texture before conditioning. After conditioning, the sludge flocs become smaller, and many irregular pores are formed on the surface, which facilitates the passage of internal moisture. Economic analysis showed that Fe2++PMS conditioning is more economical than the traditional Fenton method.