Residual Sludge Research Articles

Integral evaluation of production safety and genotoxicity of recycling residual sludge for drinking water treatment plants

ABSTRACT Recycling residual sludge in drinking water treatment plants (DWTPs) may release excessive heavy metals and organic matter, which are substances of concern because of their toxic and carcinogenic potential. The aim of this study was to investigate potential genotoxic, cytotoxic, and mutagenic effects of recycled residual sludge in terms of quality of water in potable water works. Genotoxic effects of reusing residual sludge were evaluated using: the Ames test, sperm abnormality test in mice, micronucleus assay, comet assay, and single-cell gel electrophoresis assay. The results of the Ames assay show that the disinfected water sample displays bacteriostasis at a dose of 7 L/dish regardless of treatment styles, but mutagenicity ratio (MR) < 2 can still be judged as negative. The micronucleus rates of conventional treatment were slightly genotoxic but only at 4 and 40 L/kg·bw, whereas micronucleus rates of filtered water and disinfectant from the recycling process were negative in all of the dose groups. The levels of DNA damage that are caused by different treatment processes were equivalent. Reusing residual sludge for DWTPs did not contribute to the release of genotoxic or mutagenic compounds, but it did have a remarkable effect on saving the drug dose and increasing drinking water yield. Thus, reusing residual sludge for DWTPs should be widely recommended.

The Removal of Residual Concentration of Hazardous Metals in Wastewater from a Neutralization Station Using Biosorbent-A Case Study Company Gutra, Czech Republic.

This article deals with the possibility of using a biosorbent in the form of a mixture of cones from coniferous trees to remove the residual concentration of hazardous metals contained in hazardous waste, which is disposed of in a neutralization station. The efficiency of the tested biosorbent in removing Ni, Zn, Cu, and Fe was monitored here. Laboratory research was carried out before the actual testing of the biosorbent directly in the operation of the neutralization station. With regard to the planned use of the biosorbent in the operational test, the laboratory experiments were performed in a batch mode and for the most problematic metals (Ni and Zn). The laboratory tests with real wastewater have shown that the biosorbent can be used to remove hazardous metals. Under the given conditions, 96% of Ni and 19% of Zn were removed after 20 min when using NaOH activated biosorbent with the concentration of 0.1 mol L−1. The inactivated biosorbent removed 93% of Ni and 31% of Zn. The tested biosorbent was also successful during the operational tests. The inactivated biosorbent was applied due to the financial costs. It was used for the pre-treatment of hazardous waste in a preparation tank, where a significant reduction in the concentration of hazardous metals occurred, but the values of Ni, Cu, and Zn still failed to meet the emission limits. After 72 h, we measured 10 mg L−1 from the original 4,056 mg L−1 of Ni, 1 mg L−1 from the original 2,252 mg L−1 of Cu, 1 mg L−1 from the original 4,020 mg L–1 of Zn, and 7 mg L−1 from the original 1,853 mg L−1 of Fe. However, even after neutralization, the treated water did not meet the emission limits for discharging into the sewer system. The biosorbent was, therefore, used in the filtration unit as well, which was placed in front of the Parshall flume. After passing through the filtration unit, the concentrations of all the monitored parameters were reduced to a minimum, and the values met the prescribed emission limits. The biosorbent was further used to thicken the residual sludge in the waste pre-treatment tank, which contributed to a significant reduction in the overall cost of disposing of residual hazardous waste. This waste was converted from liquid to solid-state.

Treatment of high strength wastewater by thermophilic aerobic membrane reactor and possible valorisation of nutrients and organic carbon in its residues

The depletion of nitrogen and phosphorus represents a significant problem. Two real high strength wastewaters were treated by Thermophilic Aerobic Membrane Reactor (TAMR), an advanced biological process, obtaining significant removal of pollutants. Unlike the previous works, this paper does not focus on the optimization of the performance of the TAMR, but it studied the possible reuses of liquid (permeate) and solid (biological excess sludge) matrices to recover organic carbon, nitrogen and phosphorus and promote a circular economy model. The high nitrogen content of permeate can be exploited stripping ammonia with performances higher than 80% in best conditions to produce ammonium sulphate (useful as fertilizer). Moreover, the respiromeric tests demonstrated that permeate can be used in conventional active sludge systems as external source of organic carbon granting similar denitrification rate as methanol. In the sludge residue extracted from TAMR a significant presence of organic carbon and phosphorus (as hydroxyapatite) were revealed demonstrating the feasibility of recover this residue in land application. A preliminary management costs estimation showed that TAMR, coupled with a stripping and adsorption system to recover nutrients, is economically sustainable.

Hydrothermal oxidation method to synthesize nitrogen containing carbon dots from compost humic acid as selective Fe(III) sensor

Residual sludge which is generated as a by-product during wastewater treatment needs efficient and environmentally friendly disposal. In this work, nitrogen containing carbon dots (N-CDs) was synthesized via one-step hydrothermal oxidation of humic acid for the first time, which was alkalinely extracted from the compost of sludge. The successful doping of the functional groups (hydroxyl, carboxyl and amino) on the surface of N-CDs were characterized by x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The optical properties of the synthetic N-CDs were obtained from Ultraviolet-visible spectroscopy and Photoluminescence spectra. The N-CDs had an average diameter at 1.88 nm and exhibited a well-defined spherical shape. The aqueous solution of N-CDs with excitation-dependent properties showed a strong blue emission with 8.8% quantum yield (QY) under an excitation wavelength of 340 nm, which indicate the synthesized N-CDs a promising sensing probes for iron ions in aquatic system. Moreover, the mechanism of the N-CDs sensing technique was investigated in detail, which can be explained by the fluorescence static quenching effect and a ground-state complex formed in this process. This research demonstrates an extremely sensitive method for detecting heavy metal Fe3+ at a lower 1.9 nM level by using N-CDs as fluorescent probes without a complicated procedure.

Optimisation for enhancing sludge dewaterability using different conditioners

Dewatering of alum sludge from drinking-water plants is proving to be a major challenge because of the large amounts of residual sludges produced annually. In the last few years, most studies have focused on improving the dewatering process to reduce costs of alum sludge management and transport. In the present study, three different types of conditioners were tested. Lime was used as an example of an inorganic conditioner, ferric chloride (FeCl3) was used as an example of a chemical conditioner and chitosan was used as an example of a biopolymer. The performance of a conditioner was evaluated with respect to its effect in reducing the resistance of the conditioned sludge to filtration, namely the specific resistance to filtration (SRF). Tests are run using different concentrations of the conditioners, different speeds of rotation and different pH values to investigate the maximum value of percentage reduction in SRF. The response surface methodology was chosen from the Design-Expert program (version 12), and the Box–Behnken design was employed to find factor settings that optimise the output response – that was, percentage reduction in SRF (Red. %). The model obtained proved to be significant enough but with varying degrees. Chitosan showed to be the most favourable conditioner with a maximum percentage reduction in SRF of 98.57%. This was followed by ferric chloride, which gave a value of 89.2% for percentage reduction in SRF, and lastly came lime with a percentage reduction of 79.81%. Besides, a lower concentration of the conditioner and a lower speed of rotation are required when using chitosan as a conditioner.

Occurrence and distribution of five antibiotic resistance genes during the loading period in sludge treatment wetlands

The objectives of this study were to clarify the distribution as well as the removal mechanism of antibiotic resistance genes (ARGs) within three sludge treatment wetlands (STWs) during a loading period of two years. Three STW units were constructed and run during the loading period: Unit 1 (U1) built with aeration tubes, Unit 2 (U2) built with aeration tubes and reeds, and Unit 3 (U3) built with reeds only. All targeted ARGs, intI1, and 16S rRNA were detected in residual sludge in the order of magnitude: 16S rRNA>sul1>intI1>sul2>tetC>tetA>ermB. The abundance of the five targeted ARGs, intI1, and 16S rRNA increased in residual sludge, during the loading period, which may be due to the increase in bacteria caused by the continuous import of exogenous nutrients. However, STWs can also remove ARGs from sewage during the loading period and the mean removal efficiency of five resistance genes was 73.0%. The removal rates of intI1 and 16S rRNA were 73.5% and 78.6%, respectively. Positive correlations were detected in abundance of most ARGs and intI1, as well as 16S rRNA (P < 0.05), indicating intI1 plays a vital part in the propagation of ARGs. The removal of bacteria harboring these genes also occurs in the STW units.

Sustainable management of biological solids in small treatment plants: overview of strategies and reuse options for a solar drying facility in Poland

The issue of sustainable management of biosolids (excess sludge) from wastewater treatment is an important issue in the entire developed world. Residual sludge disposal costs and environmental impact may be significant, and reducing such costs, as well as the energy consumption for dewatering and drying, is a key issue for safe and sustainable sludge disposal, considering the recent ban of some disposal options, such as landfilling, in many European countries. An alternative to thermal technologies is solar drying (not to be confused with bio-drying, very close to the concept of composting). Solar greenhouse drying technology is characterized by reduced land requirements compared with traditional outdoor drying beds, as well as by low-energy requirements compared with other thermal drying methods. Process operation is cost-efficient, with close to no maintenance, and observed specific evaporation rates up to threefold higher than conventional drying beds. Many applications of this technology exist in Poland, Germany and Austria: more than 10,000 t of wet sludge per year is treated in this way in Germany alone and almost as many (9000 t/year) in Poland. This paper examines current biosolids treatment technologies applicable to small wastewater treatment plants (2000–9999 population equivalents served) and opportunities for possible solids reuse in Poland in view of sustainable circular economy schemes. In particular, a purely solar-driven greenhouse facility for sewage sludge drying was investigated under different conditions (season, temperature, environmental humidity) and possible improvements for its efficiency evaluated. Sludge processed by solar drying could have different final disposal pathways, according to season, in accordance with the prescriptions of the new National Waste Management Plan of Poland.

Catalytic Cracking of Heavy Crude Oil over Iron-Based Catalyst Obtained from Galvanic Industry Wastes

Sewage sludge from the galvanic industry represents a problem to the environment, due to its high metal content that makes it a hazardous waste and must be treated or disposed of properly. This study aimed to evaluate the sludge from three galvanic industries and determine its possible use as catalysts for the synthesis of materials. Catalyst was obtained from a thermal process based on dried between 100–120 °C and calcination of sludges between 400 to 700 °C. The physical–chemical properties of the catalyst were analyzed by several techniques as physisorption of N2 and chemisorption of CO of the material. Catalytic activity was analyzed by thermogravimetric analysis of a thermo-catalytic decomposition of crude oil. The best conditions for catalyst synthesis were calcination between 400 and 500 °C, the temperature of reduction between 750 and 850 °C for 15 min. The catalytic material had mainly Fe as active phase and the specific surface between 17.68–96.15 m2·g−1, the catalysts promote around 6% more weight-loss of crude oil in the thermal decomposition compared with assays without the catalyst. The results show that the residual sludge of galvanic industries after thermal treatment can be used as catalytic materials due to the easiness of synthesis procedures required, the low E-factor obtained and the recycling of industrial waste promoted.

Selective Recovery of Manganese from Anode Sludge Residue by Reductive Leaching

Manganese-containing anode sludge is a common side-product in the electrowinning of zinc. The anode sludge consists mainly of oxidized manganese, but also lesser amounts of lead, calcium, and other minor metals. The impurities present in the anode sludge mandate new recycling strategies for its efficient use. This work demonstrates a novel method for selective manganese recovery from lead- and calcium-bearing manganese oxide solid residue. Leaching with sulfuric acid in the presence of a selected reducing agent, such as hydrogen peroxide or citric acid, yields a concentrated MnSO4 solution with high selectivity over calcium and lead. Manganese yields up to 98% can be obtained. Minimization of calcium and lead in final manganese product can be accomplished with the correct choice of leaching conditions. Alongside manganese sulfate solution, leaching residue with high content of lead and silver was also formed.

Hydrothermal Carbonization as a Strategy for Sewage Sludge Management: Influence of Process Withdrawal Point on Hydrochar Properties

Conventional activated sludge systems, still widely used to treat wastewater, produce large amounts of solid waste that is commonly landfilled or incinerated. This study addresses the potential use of Hydrothermal Carbonization (HTC) to valorize sewage sludge residues examining the properties of hydrochars depending on HTC process conditions and sewage sludge withdrawal point. With increasing HTC severity (process residence time and temperature), solid yield, total Chemical Oxygen Demand (COD) and solid pH decrease while ash content increases. Hydrochars produced from primary (thickened) and secondary (digested and dewatered) sludge show peculiar distinct properties. Hydrochars produced from thickened sludge show good fuel properties in terms of Higher Heating Value (HHV) and reduced ash content. However, relatively high volatile matter and O:C and H:C ratios result in thermal reactivity significantly higher than typical coals. Both series of carbonized secondary sludges show neutral pH, low COD, enhanced phosphorous content and low heavy metals concentration: as a whole, they show properties compatible with their use as soil amendments.

Application of MBR Technology in Schoolyard Domestic Sewage Treatment

This paper discusses the special features of campus sewage, and chooses more suitable sewage treatment for campus sewage. At the same time, it expounds the advantages and disadvantages of it. Compared with city sewage from industry and agriculture, campus sewage has much more characteristic content of pollutants with higher COD, SS and tiny toxic pollutants[5]. Therefore rather than using the traditional activated sludge process, MBR is more appropriate for schoolyard domestic sewage treatment for small area, stable effluent quality, good removal efficiency and little residual sludge production. Additionally, new campuses of universities are always built far away from the city centre, and the water transportation cost can be saved with a sewage treatment system in the campus. The treated water has the quality to be used as gray water for campus watering, cleaning and so on, which can also help the universities to save money. Undeniably, it also has the disadvantages of high energy consumption and cost, for it needs to update the active membrane regularly. If it is used in cities, it will be a huge financial burden for governments. But when it is used in campuses, less sewage will need less membranes, and the polluted membranes can also be used for students’ research.

Applied Cleaning Methods of Oil Residues from Industrial Tanks

The oil industry is facing a major problem with the large amount of oil residue generated in the tanks that store and process crude oil or its products. Research has shown that the residues of petroleum sludge, which according to a sample from the Azzawiya oil refinery in Libya mainly consist of oil, water and solid residues in 42.8%, 2.9% and 55.2% respectively, result in the alteration of the product quality and reduced capacity of the tanks. The solution for this problem as well as the need for inspection and maintenance requires the removal of this oil sludge and the internal cleaning of the tanks. This report aims to review the applied clean-up methods available in the world market and to identify the most efficient, safest, most economical and most environmentally friendly cleaning process. It must be noted that until now, there is not any published work which presents the applied techniques. To accomplish this goal, a total of five manual, automatic and robotic cleaning systems were analyzed and evaluated according to their advantages and disadvantages. The results show that the MEGAMACS with sludge extractor automatic cleaning system with an output of 14.8 m3/h is the fastest cleaning system, while the MARTin where the presence of people inside the tank is not necessary at any stage is the safest. In terms of cleaning costs and environmental impact, the automated BLABO, COW and MEGAMACS systems as well as the MARTin robotic system are the most economical and environmentally friendly due to the closed cleaning circuit and the ability to recover up to 95% of the oil from the sludge, which is returned to the customer and the earnings cover the costs of cleaning. The conclusion drawn is that the current need in the oil industry, in the field of tank cleaning, is the use of high-efficiency automatic or robotic cleaning methods, which aim to reduce the tank downtime, without the need for staff entrance into a permit-required confined space and with the ability to recover up to 100% of the hydrocarbons present in the composition of the sludge.

ESTABILIZACIÓN POR VERMICOMPOSTEO DE LODOS RESIDUALES APLICADOS EN LA PRODUCTIVIDAD DE ALBAHACA (Ocimum basilicum L.)

Sewage sludge, a byproduct of wastewater treatment, accumulates a high content of organic matter, heavy metals and other toxic compounds. Due to its accelerated generation, adequate management is necessary for its stabilization and disposal. Vermicomposting is a management alternative that stabilizes residual sludge and allows its addition to the soil, improving structural properties and increasing its fertility. The objective of this study was to evaluate the effect of vermicompost of sewage sludge and equine manure on the productivity and antioxidant activity of basil plants ( Ocimum basilicum L.). Vermicompost was developed in a 30:70 proportion of sewage sludge and equine manure, and the effect on basil was evaluated under different doses of vermicompost (20, 40 and 60 t/ha). The use of vermicompost significantly increased the growth rate, without causing effects on the antioxidant activity and the content of phenolic compounds in basil plants.

Using Portland Cement to Stabilize/Solidify Sludge Residue from Treatment of Cardboard Plant Wastewater

Abstract This work presents the stabilization/solidification (S/S) process by substituting the portland mortar cement fractions by sludge. This sludge results from the wastewater treatment process ...

From pre-treatment to co-treatment - How successful is ultrasonication of digested sewage sludge in continuously operated anaerobic digesters?

The present study assessed the performance of ultrasonic co-treatment, i.e., the treatment of digested sewage sludge in continuously operated anaerobic digesters. Experiments were carried out using a non-sonicated control digester and a sonicated test digester. The test digester received side-stream sonication (∼10% of reactor volume per day) at a specific energy input of 2,000 kJ/kgTS. Treatment effects were monitored based on (i) specific methane production, (ii) (volatile) solids removal, and (iii) digestate dewaterability. Results revealed that co-treatment significantly enhanced average methane production (+6%), volatile solids removal (+9%), and solids reduction in the digestate (−5%). However, due to the only moderate enhancement and the relatively high energy input, the average cost recovery (i.e., the ratio between electricity costs and benefits due to additional methane and improved solids removal) was only 6%–9%, depending on the assumed disposal costs. Moreover, as sonication led to impaired digestate dewaterability (average increase in normalized capillary suction time of 14%), the cost recovery due to reduced residual sludge might be negated again by lower dewatering efficiency. Overall, co-treatment seemed not economical under the conditions investigated. To render co-treatments economically feasible, further research, especially exploring the potential of low energy input sonication, is required.

Integrated life-cycle data envelopment analysis for techno-environmental performance evaluation on sludge-to-energy systems

Sludge-to-energy systems have been widely recognized as a favourable approach to treat sewage sludge and recover energy from the energy-rich biomass waste simultaneously. An inclusive efficiency benchmarking tool for sludge-to-energy systems is lacking. This study developed a life-cycle data envelopment analysis framework, by integrating life-cycle assessment and data envelopment analysis, for evaluating sludge-to-energy systems. The life-cycle data envelopment analysis approach highlighted the strong linkage between sludge treatment and energy systems and included all the essential performance metrics in benchmarking the efficiency of the sludge-to-energy systems. Using life-cycle data envelopment analysis, this study compared the relative operation efficiency of nine Hong Kong sludge-to-energy systems and seven systems in other urban cities based on the volatile solids reduction, energy recovery, energy use, chemical consumption, sludge residues generation and direct environmental emissions. The results showed that 44% and 69% of the sixteen sludge-to-energy systems were efficient in terms of overall and pure technical efficiency, respectively. The life-cycle data envelopment analysis results also informed the appropriate strategies for improving efficiency, such as increasing energy recovery, reducing energy use and scaling up/down the systems, for the less efficient systems. The life-cycle data envelopment analysis framework is widely applicable for guiding decision-making on enhancing sludge-to-energy systems worldwide.

Recovery of nutrients from fish sludge in an aquaponic system using biological aerated filters with ceramsite plus lignocellulosic material media

The recovery of nutrients from residual fish sludge in aquaponics could achieve zero solid waste discharge and supplement additional nutrients to hydroponics, thus yielding environmental and economic benefits. In this study, novel biological aerated filters (BAFs) with ceramsite plus different lignocellulosic materials (corn straw, wheat straw, and sawdust) are designed and installed in aquaponic systems. The BAFs performed the fish sludge separation and nutrient conversion in a single equipment without the necessity for backwashing. The potential for nutrient recovery from fish sludge is evaluated by comparing four BAFs filled with different media. The BAF with ceramsite plus sawdust achieves the highest mineralization capacity based on nitrification and dissolved total phosphorus. The average concentrations of N, P, K, Ca, Mg, and S macronutrients reach 12.3%, 11.8%, 4.5%, 26.4%, 22.6%, and 46.0% of those of Hoagland nutrient solution, respectively. The recovered Fe, Mn, and B micronutrients are 10.0%, 12.0%, and 18.0%, respectively, whereas Cu, Zn, and Mo are 1.5, 1.8, and 1.0 times, respectively, of those of Hoagland nutrient solution. The estimated nutrient recoveries of Ca, Mg, and S have good performance efficiencies, followed by K and Cu; those of N, P, Fe, Mn, and Zn have potentials for further improvement. The modified aquaponics with BAFs are proposed for the recovery of both dissolved and solid nutrients.

GRAIN YIELD AND MICROBIOLOGICAL QUALITY OF COWPEA PLANTS GROWN UNDER RESIDUAL EFFECT OF SEWAGE SLUDGE FERTILIZATION1

ABSTRACT Cowpea plants produce protein-rich grains and present high yield potential when grown under irrigation and organic fertilization, enabling to substitute part of the mineral fertilizer with sewage sludge, reducing costs and generating environmental benefits. Thus, a field study about residual effect of sewage sludge fertilization on cowpea was developed to evaluate this substitution. The experiment was conducted using a randomized block design with four replications, in a 2×5 factorial arrangement consisted of two fertilization types (residual effect of sewage sludge fertilization, and mineral fertilizers) and five cowpea cultivars (BRS-Pajeu, BRS-Xiquexique, BRS-Marataoa, BRS-Pujante, and BRS-Cauame). The residual fertilizations were from applications of sewage sludge and NPK mineral fertilizers for pineapple crops grown in the area before the cowpea crop. The experiment was conducted using 80,000 plants ha-1 and micro-sprinkler irrigation. Vegetative and yield components, grain yield, and microbiological quality were analyzed. BRS-Pujante had the highest cowpea grain yield (4,124 kg ha-1) and the highest means for vegetative and yield components. The soil with residual sewage sludge fertilization improved the cowpea root growth and grain yield (3,854 kg ha-1); the latter was 19% higher than that of treatments with mineral fertilization. These results were related to the great soil organic matter content provided by the sludge fertilization, which promotes nutrient mineralization, increasing grain yield. Fresh and dry grains of cowpea plants grown under residual effect of sewage sludge fertilization have similar microbiological quality to those of plants grown under mineral fertilization.

The effect of bioaugmentation with Exiguobacterium sp. AO-11 on crude oil removal and the bacterial community in sediment microcosms, and the development of a liquid ready-to-use inoculum

This study demonstrates the feasibility of using Exiguobacterium sp. AO-11 to remediate oil-contaminated environments. Bioaugmentation using AO-11 showed the best removal percentage, 75%, of 4% (w/w) crude oil in sediment microcosms in 100 days. In terms of the bacterial community structure during crude oil degradation, the addition of AO-11 did not change the indigenous bacterial community, while the addition of urea fertilizer induced structural shift of indigenous bacterial community. Exiguobacterium sp. AO-11 was developed as a bioremediation product, and a liquid formulation of AO-11 was developed. Coconut milk residue and soybean oil mill sludge were used for bacterial cultivation to reduce the production cost, and they could enhance bacterial cell growth. The liquid formulation of AO-11 prepared in phosphate buffer could be stored at 4 °C for at least 2 months, and it maintained efficacy in the treatment of crude oil-contaminated seawater. Overall, bioaugmentation with strain AO-11 could be an effective solution for the bioremediation of crude oil-contaminated environments.

Sludge predation by aquatic worms: Physicochemical characteristics of sewage sludge and implications for dewaterability

Worm predation is an eco-friendly and low energy cost means of sludge reduction that has shown great promise. The worm predation process consists of inoculating specific species of aquatic worms into the sludge system to build a suitable biotope. After predation, the residual sludge needs to be discharged and disposed. This study investigates the potential effects of worm predation on sludge dewatering focusing on the mechanisms, characteristics of sedimentation, filtration and dewatering for the sludge from the predation process. It also describes the changes in extracellular polymeric substance and bound water, and discusses options to improve sludge dewatering. The results suggested that worm predation restrained the viscosity and surface charge of residual sludge and helped prevent sludge bulking. However, sludge filterability deteriorated when predation occurred. The residual sludge experienced a significant reduction in the contents of loosely bound and tightly bound extracellular polymeric substances and a decreased ratio of protein to polysaccharides content during the five days of predation. Extending the sludge retention time of predation to five days contributed to a release of bound water and synergistically improved centrifugal dewatering of the residual sludge with ferric chloride added as conditioner.