Influence of wastewater treatment on sludge production and processing

The challenge of stricter wastewater standards is resulting in configuration changes to wastewater treatment. As facilities upgrade, the type of sludge produced is changing, with growing quantities of secondary and chemical sludge at the expense of primary sludge. It is already understood that secondary sludge is harder to treat than its primary equivalent; therefore, increasing the quantity of this type of sludge will have detrimental impacts downstream. As legislation tightens further, extended aeration times may be required during processing to remove more nutrients. Work has shown that extended aeration further exacerbates the treatability of secondary sludge. This paper explains how tightening wastewater legislation fundamentally alters the nature of the sludge produced, and how these alterations impact further processing, especially with respect to sludge production and type; sludge energy content; performance of anaerobic digestion and dewatering, and potential for thermal energy recovery.     

Quantification and molecular characterization of enteric viruses detected in effluents from two hospital wastewater treatment plants

Hospital wastewater has been described as an important source of spreading pathogenic microorganisms in the environment. However, there are few studies reporting the presence and concentrations of gastroenteric viruses and hepatitis A viruses in these environmental matrices. The aim of this study was to assess the contamination by viruses responsible for acute gastroenteritis and hepatitis derived from hospital wastewater treatment plants (WWTPs). Rotavirus A (RV-A), human adenoviruses (HAdV), norovirus genogroup I and II (NoV GI/GII) and hepatitis A viruses (HAV) were detected and quantified in sewage samples from two WWTPs located in Rio de Janeiro (Brazil) that operates different sewage treatments. WWTP-1 uses an Upflow Anaerobic Sludge Blanket (UASB reactor) and three serial anaerobic filters while WWTP-2 uses aerobic processes, activated sludge with extended aeration and final chlorination of the effluents. Viruses’ detection was investigated by using conventional PCR/RT-PCR, quantitative real-time PCR (qPCR) and partial sequencing of the genome of the viruses detected. Rate of viruses detection ranged from 7% (NoV GI in WWTP-1) to 95% (RV-A in WWTP-2) and genome from all viruses were detected. The most prevalent genotypes were RV-A SG I, HAdV species D and F, NoV GII/4 and HAV subgenotype IA. Mean values of viral loads (genome copies (GC)/ml) obtained in filtered effluents from anaerobic process was 1.9 × 10³ (RV-A), 2.8 × 10³ (HAdV) and 2.4 × 10³ (NoV GII). For chlorinated effluents from activated sludge process, the mean values of viral loads (GC/ml) was 1.2 × 10⁵ (RV-A), 1.4 × 10³ (HAdV), 8.1 × 10² (NoV GII) and 2.8 × 10⁴ (HAV). Data on viral detection in treated effluents of hospital WWTPs confirmed the potential for environmental contamination by viruses and could be useful to establish standards for policies on wastewater management.     

A septic tank‐UASB combined system for domestic wastewater treatment: a pilot test

A 250 L and a 550 L pilot scale Up‐Flow Anaerobic Sludge Blanket (UASB) reactors having different reactor height were fed septic tank effluents and operated at ambient temperatures of 0°C to 30°C. Both UASB reactors were fed intermittently at least 8 times per Hydraulic Retention Time (HRT) and the performance was monitored at 4d and 1d HRT. The removal efficiencies of Total Suspended Solid (TSS) and Total Chemical Oxygen Demand (COD_t) were about 59–68% and 54–59%, respectively, for both reactors at both HRT. The TSS and CODt removal efficiencies of Septic tank – UASB combined system were above 80% for both HRTs tested. The average biogas yields were almost same at 4d and 1d HRT, representing 31(±3)% of influent CODt. The nitrogen and phosphorous removal efficiency was an average 20–30%. The tested system can become a suitable low cost yet effective option.     

Post‐treatment of up‐flow anaerobic sludge blanket reactor effluents in activated sludge process‐based system for anionic surfactants

This paper presents the performance of two full‐scale up‐flow anaerobic sludge blanket–activated sludge process (UASB‐ASP)‐based sewage treatment plants (STPs) (surface and diffused aeration‐based activated sludge processes as post‐treatment units). Performance of this combination is compared with UASB–polishing ponds and UASB–ozonation‐based STPs. Post‐treatment units removed 89 and 92% of anionic surfactants (AS) by surface and diffused aeration, respectively. Finally, 0.61 and 0.23 mg/L of AS were discharged from post‐treatment steps after overall reduction of 90–92%. Final concentrations from UASB‐ASP‐based STPs were low compared with UASB–polishing ponds (3.60–4.91 mg/L) and UASB–ozonation (1.52 and 0.53 mg/L). Overall, UASB‐ASP‐based STPs were working efficiently for the removal of organics in terms of chemical oxygen demand (COD) (84%) and biochemical oxygen demand (BOD) (93%), but they need further modifications for the removal of AS up to the level of risk quotient [risk quotient (RQ)] ≤ 1 for no risk to aquatic environment.     

Effects of hydraulic retention time and proteins on sludge toxicity for 4‐chlorophenol wastewater treatment in sequencing batch reactors

Due to the higher uncertainty of environmental risk for pollutants’ treatment by activated sludge, 10 mg/L influent 4‐chlorophenol (4‐CP) treated via a sequencing batch reactor (SBR) was used as acclimated SBR. Another SBR was used as control SBR without 4‐CP. The effects of hydraulic retention time (HRT) and proteins on sludge toxicity for 4‐CP treatment were analysed, and compared to the control SBR. Results showed that the sludge toxicity in acclimated SBR was significantly higher than that of the control SBR. Shortening HRT from 12 to 8 hours was beneficial to degrade 4‐CP and lower sludge toxicity. The identified highly expressed protein of ABC transporter co‐existed in control and acclimated SBRs, while other proteins of TonB‐dependent receptor, heat shock 70 kDa protein and superoxide dismutase in acclimated sludge were overexpressed relative to the control sludge, which played an important function in degrading 4‐CP, resisting 4‐CP toxicity and eliminating sludge toxicity.     

Assessment of wastewater treatment technologies: life cycle approach

Four municipal wastewater treatment plants (WWTPs) in India based on different technologies are compared by conducting Life Cycle Assessment (LCA) using field data. CML 2 baseline 2000 methodology is adopted in which eight impact categories are considered. SBRs ranked highest in energy consumption and global warming potential (GWP) but also produced the best effluent with respect to organics and nutrients. Constructed wetlands have negligible energy consumption and negative GWP because of carbon sequestration in the macrophytes. Emissions associated with electricity production required to operate the WWTPs, emissions to water from treated effluent and heavy metal emissions from waste sludge applied to land are identified as main contributors for overall environmental impacts of WWTPs. This comparison of technologies suggests that results from LCA can be used as indicators in a multicriteria decision‐making framework along with other sustainability indicators.     

A novel application of TPAD-MBR system to the pilot treatment of chemical synthesis-based pharmaceutical wastewater

A pilot-scale test was conducted with a two-phase anaerobic digestion (TPAD) system and a subsequential membrane bioreactor (MBR) treating chemical synthesis-based pharmaceutical wastewater. The TPAD system comprised a continuous stirred tank reactor (CSTR) and an upflow anaerobic sludge blanket-anaerobic filter (UASBAF), working as the acidogenic and methanogenic phases, respectively. The wastewater was high in COD, varying daily between 5789 and 58,792 mg L(-1), with a wide range of pH from 4.3 to 7.2. The wastewater was pumped at a fixed flow rate of 1m(3)h(-1) through the CSTR, the UASBAF and the MBR in series, resulting in respective HRTs of 12, 55 and 5h. Almost all the COD was removed by the TPAD-MBR system, leaving a COD of around 40 mg L(-1) in the MBR effluent. The pH of the MBR effluent was found in a narrow range of 6.8-7.6, indicating that the MBR effluent can be directly discharged into natural waters. A model, built on the back propagation neural network (BPNN) theory and linear regression techniques, was developed for the simulation of TPAD-MBR system performance in the biodegradation of chemical synthesis-based pharmaceutical wastewater. The model well fitted the laboratory data, and was able to simulate the removal of COD.     

A comparative study on treatment of wastewaters with various biodegradability and various pH values using single‐chamber microbial fuel cells

This work assessed the performance of a single‐chamber microbial fuel cell (MFC) with various substrates. Primary settled domestic wastewaters were used to simulate wastewaters of high biodegradability; while phenol‐based wastewaters and benzene‐based wastewaters were used to simulate wastewaters of low biodegradability. Experiments were performed at initial pH values of 6, 7 and 8. The maximum voltage production, power density and removal of substrate were obtained using primary settled domestic wastewater, whereas the lowest values were obtained using phenol‐based wastewater. The maximum chemical oxygen demand removal efficiency, phenol removal efficiency and benzene removal efficiency were 80.8, 63.3 and 77.8%, respectively. The performance of the MFC was enhanced by increasing the influent pH. The lowest coulombic efficiencies were obtained from phenol‐based wastewater and benzene‐based wastewater, which indicated that electrogenic bacteria were not the primary microorganisms responsible for the biodegradation of low biodegradable wastewater.     

Performance of an up-flow anaerobic stage reactor (UASR) in the treatment of pharmaceutical wastewater containing macrolide antibiotics

The performance of an up-flow anaerobic stage reactor (UASR) treating pharmaceutical wastewater containing macrolide antibiotics was investigated. Specifically, it was determined whether a UASR could be used as pre-treatment system at an existing pharmaceutical production plant to reduce the antibiotics in the trade effluent. Accordingly, a UASR was developed with an active reactor volume of 11 L being divided into four 2.75 L stages. Each stage of the reactor was an up-flow sludge blanket reactor and had a 3-phase separator baffle to retain biomass. The reactor was fed with real pharmaceutical wastewater containing Tylosin and Avilamycin antibiotics and operated with step-wise increases in the reactor organic loading rate (OLR) from 0.43 to 3.73 kg chemical oxygen demand (COD) m(-3)d(-1), and then reduced to 1.86, over 279 days. The process performance of the reactor was characterised in terms of its COD removal, Tylosin reduction, pH, VFA production, methane yield and sludge washout. At a total hydraulic retention time (HRT) of 4 d and OLR of 1.86 kg COD m(-3)d(-1), COD reduction was 70-75%, suggesting the biomass had acclimated to the antibiotics. Furthermore, an average of 95% Tylosin reduction was achieved in the UASR, indicating that this antibiotic could be degraded efficiently in the anaerobic reactor system. In addition, the influence of elevated Tylosin concentrations on the UASR process performance was studied using additions of Tylosin phosphate concentrate. Results showed similar efficiency for COD removal when Tylosin was present at concentrations ranging from 0 to 400 mgL(-1) (mean removal over this range was 93%), however, at Tylosin concentrations of 600 and 800 mgL(-1) there was a slight decline in treatment efficiency at 85% and 75% removal, respectively.     

Coupling of sequencing batch reactor and mesh filtration: operational parameters and wastewater treatment performance

Wastewater treatment performance of the combined process of sequencing batch reactor (SBR) and mesh filtration bio-reactor was investigated with a synthetic wastewater. In this system, the filtration was performed only by the water level difference between the reactor and the effluent port, with the help of a sludge layer which accumulated on the mesh filter.

A half volume of the mixed liquor was filtrated for ca. 1 h, and the filtration time was not affected by the initial pressure within the range of 0.5–2.0 m-H₂O. Since the mesh filter could effectively reject the biomasses in the reactor, the effluents contained SS of less than 1 mg/L and BOD of less than 10 mg/L under continuous or intermittent aeration conditions. Nitrogen was also removed effectively with the adjustment of aeration time under the intermittent aeration conditions.

The results obtained in this work indicate that mesh filtration could be effectively combined with SBR and improve the performance of SBR.

In addition, it was shown that the performance of the mesh filtration such as filtration time and solids separation was influenced significantly by the saccharide content in the exocellular polymer of the activated sludge.     

Simulation of closed double‐sludge retention time anoxic‐oxic process in wastewater treatment: case study for a utility model process

The ‘closed double‐sludge retention time anoxic‐oxic (SRT AO) process’ is a utility model designed by the Shanghai Urban Construction Design and Research Institute. It can quantitatively control the nitrification level by adjusting wastewater distribution and mixed sludge return during wastewater treatment, and can thus considerably reduce construction investment and operation costs. However, mixed sludge return from the sedimentation tank may dilute the concentration of nitrobacteria because the heterotrophic bacteria propagate faster. In this paper, the closed double‐SRT AO process was modelled and simulated based on its application at the Zhuyuan Second Wastewater Treatment Plant (WWTP). The distribution ratio was found to have a significant influence on the nitrobacteria's concentration but does not eliminate the existence of nitrobacteria in the system. Extension of sludge age enhanced the heterotrophic bacteria concentration and to a greater extent the nitrobacteria concentration, thus attenuated the dilution of nitrobacteria. Mixed liquid recycling showed little effect on nitrobacteria concentration. The closed double‐SRT AO process in Zhuyuan Second WWTP had enough capacity for complete nitrification, but the shortage of organic matter in the influent impeded the nitrogen removal.     

Improve effluent water quality at Abu‐Rawash wastewater treatment plant with the application of coagulants

This research investigated a process to improve the Abu‐Rawash WWTP effluent water quality with the application of aluminum chloride (AlCl₃); in turn, this improvement will lead to improve water quality at the El‐Rahawy drain and in the Rosetta branch of the Nile River. Sewage samples were collected from the effluent of the grit removal chamber. Jar tests were performed to estimate the coagulant dosage required to obtain acceptable treatment. To prove the efficiency of the AlCl₃ in wastewater treatment, a comparison was conducted between AlCl₃ and other common coagulants used in wastewater treatment which include ferrous sulfate (FeSO₄), ferric sulfate (Fe₂(SO₄)₃) and ferric chloride (FeCl₃). Results showed AlCl₃ was more cost‐effective and efficient in wastewater treatment than these three iron‐based coagulants. A paired‐sample t‐test was also performed to rank the performance of the various coagulants tested. The t‐test has also confirmed that the AlCl₃ has the highest performance over those coagulants.     

An introduction of a multi‐soil‐layering system: a novel green technology for wastewater treatment in rural areas

Multi‐soil‐layering (MSL) systems are designed for municipal wastewater, livestock wastewater and polluted river water treatments. They are mainly composed of soil mixture block layers and water‐permeable layers (PL). The MSL system overcomes many of the shortcomings of conventional soil treatment systems such as easy clogging, large land requirement and low hydraulic loading rate. This paper summarizes the structure, purification mechanism and practical application of the systems for different kinds of wastewater treatment. The paper also compares MSL systems with other decentralized systems such as wetland and compact filter systems in their respective structures and treatment efficiencies. Finally, the paper gives a rough evaluation of the lifespan and cost of an MSL system based on its material composition.     

Seismic testing and numerical analysis of Y‐shaped eccentrically braced frame made of high‐strength steel

In eccentrically braced frame made of high‐strength steel (HSS‐EBF), link and brace are made from conventional steel whereas other structural members use high‐strength steel. Using HSS for beams and columns in EBF can reduce steel consumption and increase economic efficiency. In this paper, one shake table test of a 1:2 scaled three‐story Y‐shaped HSS‐EBF (Y‐HSS‐EBF) specimen was carried out to study its seismic behavior underground motions with different peak ground accelerations. The dynamic properties, base shear force, displacement, and strain responses of the specimen were obtained from this test. In addition, the finite element models of two 10‐story Y‐HSS‐EBF buildings and one 10‐story conventional Y‐EBF building were evaluated for seismic effects. Nonlinear pushover and dynamic analyses were conducted to compare their seismic performance and economy. The results indicated that the specimen exhibited sufficient lateral stiffness and safety but suffered some localized damages. During the high seismic intensity earthquakes, the links of the test specimen were in inelastic to dissipate the earthquake energy, whereas other structural members remained in the elastic state. Under the same design conditions, Y‐HSS‐EBF used less steel than that of conventional Y‐EBF, which could reduce the amount of steel used in Y‐HSS‐EBF. The Y‐HSS‐EBF is a safe, dual system with reliable seismic performance.     

Investigation of the sludge reduction mechanism in the anaerobic side-stream reactor process using several control biological wastewater treatment processes

To investigate the mechanism of sludge reduction in the anaerobic side-stream reactor (SSR) process, activated sludge with five different sludge reduction schemes were studied side-by-side in the laboratory. These are activated sludge with: 1) aerobic SSR, 2) anaerobic SSR, 3) aerobic digester, 4) anaerobic digester, and 5) no sludge wastage. The system with anaerobic SSR (system #2) was the focus of this study and four other systems served as control processes with different functions and purposes. Both mathematical and experimental approaches were made to determine solids retention time (SRT) and sludge yield for the anaerobic SSR process. The results showed that the anaerobic SSR process produced the lowest solids generation, indicating that sludge organic fractions degraded in this system are larger than other systems that possess only aerobic or anaerobic mode. Among three systems that involved long SRT (system #1, #2, and #5), it was only system #2 that showed stable sludge settling and effluent quality, indicating that efficient sludge reduction in this process occurred along with continuous generation of normal sludge flocs. This observation was further supported by batch anaerobic and aerobic digestion data. Batch digestion on sludges collected after 109 days of operation clearly demonstrated that both anaerobically and aerobically digestible materials were removed in activated sludge with anaerobic SSR. In contrast, sludge reduction in the aerobic SSR process or no wastage system was achieved by removal of mainly aerobically digestible materials. All these results led us to conclude that repeating sludge under both feast/fasting and anaerobic/aerobic conditions (i.e., activated sludge with anaerobic SSR) is necessary to achieve the highest biological solids reduction with normal wastewater treatment performance.     

Investment decision model of wastewater treatment public–private partnership projects based on value for money

Most existing studies analyse the early decision‐making processes of public–private partnership (PPP) projects from the perspective of the government or investors, as such decisions involve lengthy negotiations and are likely to lead to unfair results. Hence, there is a need for fair and reasonable investment decision‐making methods. This study investigates the investment return system of PPP wastewater treatment projects. The net present value of investment income is considered the investment decision indicator of social capital, while value for money (VFM) is the indicator of government decision‐making. Considering both yield and VFM, the system dynamics method and Vensim software are used to establish the investment decision model. A case study validates the proposed model and predicts a reasonable range of unit prices and concession periods for wastewater treatment through government–enterprise cooperation, to improve the transparency and initial decision fairness of PPP sewage treatment projects.     

Potential of using nonwoven polyester fabric (NWPF) as a packing media in multistage passively aerated biological filter for municipal wastewater treatment

The performance of a multistage passively aerated biological filter (PABF) packed with Nonwoven polyester fabric (NWPF) for municipal wastewater treatment was investigated under different operating conditions. The system was operated at different hydraulic retention times (HRTs) of 2.3, 1.72 and 1.38 h and corresponding to organic loading rates (OLRs) of 1.77, 2.15 and 2.9 kg BOD/m³. d. Increasing HRT and decreasing OLR, increased dissolved oxygen (DO) and consequently increased the removal rate of organic matters (87%), suspended solids (95.8%) and ammonia (88%). Profile results from different compartments showed that the major part of organic and suspended matters was removed in the upper layers of the system, whereas most of the suspended solids were trapped, while the nitrification process took place in the lower part of the PABF system because of the increase in DO concentrations. The results proved the advantage of using NWPF. It has pleated and rough surface which retain more biomass compared with plain surface. Excess biomass produced from PABF was negligible compared to conventional treatment systems.     

Decolourization performance and mechanism of leachate secondary effluent using Poly‐aluminium(III)–magnesium(II) sulphate

Poly‐aluminium(III)–magnesium(II) sulphate (PMAS) was used to remove the colour from the secondary effluent of landfill leachate and the decolourization mechanism was researched. The results indicated that the decolourization efficiency using PMAS was better than the decolourization that occurred using other traditional coagulants, with a colour removal >90%. X‐ray diffraction and infrared spectrometry showed that PMAS was probably a type of macromolecular composite polymer of aluminium and magnesium that was based on –OH bonds. The coagulation mechanism of PMAS was primarily charge neutralization and coprecipitation netting, with charge neutralization being the dominant mechanism at low doses. In addition, the flocculation behaviour differed in response to various pH values of wastewater at high doses. Specifically, flocculation was primarily driven by charge neutralization at a low pH and coprecipitation netting at a high pH, while it occurred via a combination of these procedures under neutral conditions.     

Wind effect of a twin‐tower super high‐rise building with weak connection

An analysis and estimation method of multibalance synchronous test is established to study the wind effect of a complex super high‐rise building with weak connection. First, the frequency domain method is applied to deduce the calculation process of the wind effect of the multitower structure on the basis of the high frequency force balance (HFFB) technique. Then, the synchronous force test of HFFB is conducted on a twin‐tower super high‐rise building connected by a bridge. The wind‐induced response and loads and the interference effect between the two towers are analyzed based on the wind tunnel test data. The displacement correlation between the towers and the relative displacement of the multitower structure are investigated. Results show that the maximum and minimum relative displacements in the along‐bridge direction are 0.26 m in the along‐wind direction and ?0.26 m in the crosswind direction, respectively. The channeling effect formed by the surrounding buildings is the main cause of the maximum cross‐bridge displacement. The influence of the correlation between the two towers can be ignored for the along‐bridge relative displacement. The results of the HFFB and high‐frequency pressure integral test agree with each other, thereby indicating the reliability and effectiveness of the proposed method.     

Three‐dimensional computer‐aided finite element method retrofitting modeling and non‐destructive testing techniques for the assessment of actual existing high‐rise fire‐damaged reinforced concrete building

Concrete is generally fire resistant. A fire in a concrete structure rarely results in a serious damage as to require substantial demolition. But, loss of the utility of a building could result in serious financial consequences for the owner, which calls for immediate reinstatement. To work out proper and efficient repair strategy, however, would require a thorough investigation of the effect of fire on the structural properties of the concrete and steel; the significance which any permanent change in material characteristics may have on the future structural performance of the member; the feasibility of repairs to compensate of any unacceptable reduction in structural performance, durability, and so on; and the influence which fire exposure of individual member may have on the performance of the entire structure. These all said tasks are dependent on the complete analysis of the fire‐damaged building. Without it, no repair works estimation, extent of repair and kind of repair can be carried out for the fire‐damaged buildings. Therefore, the impeccable analysis and design is of utmost importance for repair of such buildings after preliminary investigation of the extent of fire damages to the concrete structural members. This forms the basis of this research study, which aims at detailed analysis and design of the actual existing high‐rise fire‐damaged buildings for fire retrofitting and assessment of fire damages by non‐destructive techniques. Fire damages in buildings due to explosion, accidents or by some other reasons cause severe structural damages. The structural integrity of existing buildings is now a burning issue. Analytical, theoretical and design‐cum‐construction techniques are constantly being reviewed by government agencies and engineering consultants. Therefore, researchers are delving into this matter to find the best retrofitting techniques for fire‐damaged buildings. This paper is an outcome of such detailed research studies. It covers the actual case study of existing buildings, review of existing knowledge for fire damages and their mitigation and protective design technologies, and analytical and computational techniques, which have limited research data. In this study, Extended 3D Analysis of Building Systems (ETABS) is used as software for fire retrofitting analysis, and UBC‐97 is used as a code for the fire analysis and design. The ETABS building model is verified by manual calculations as well. Copyright © 2011 John Wiley & Sons, Ltd.