Effectiveness of breakpoint chlorination and rechlorination on nitrified chloraminated water

Chloramine is used as a secondary disinfectant in water distributions system (WDS). However, nitrification is a major concern involved in the chloraminated WDS as it leads to the accelerated decay of chloramines. After the onset of nitrification, breakpoint chlorination followed by rechlorination is generally practiced in WDS to reinstate chloramine residuals in the WDS. In this study, two different control strategies re-chlorination and breakpoint chlorination followed rechloramination were applied on the severely nitrified water collected from the laboratory-scale reactor system. Results showed that breakpoint chlorination followed by rechloramination is highly stable as the chloramine residual was maintained up to 300 hours and is highly effective than rechlorination alone as it could maintain residue only up to 50 hours even with repeated re-dosing

Training young water professionals in leadership and transdisciplinary competencies for sustainable water management in India

Young water professionals (YWPs) have a critical role in ensuring how water resources will be managed to contribute towards the 2030 Agenda for Sustainable Development. To address the challenges of climate change, population growth, and urbanization, YWPs require leadership skills, transdisciplinary competencies, technical knowledge, and practical experience. This article presents the India YWP training program, led by Western Sydney University and the Australia India Water Centre (AIWC), aimed at developing a cohort of skilled YWPs and nurturing the next generation of water leaders in support of India’s water reform agenda and the National Water Mission. The program engaged 20 YWPs, consisting of an equal gender representation, selected by the Ministry of Jal Shakti from various water management agencies and departments across India. The 11-month training program was designed to be transformative and interactive, and it used an online platform comprising online lectures, mentoring, and project-based learning facilitated by the AIWC team. The training methodology focused on engaged learning, incorporating online workshops, Situation Understanding and Improvement Projects (SUIPs), online group discussions, and mentoring. The SUIPs provided a platform for YWPs to work in pairs, receiving guidance from AIWC members, enabling them to develop practical skills and knowledge in realworld contexts. The program effectively enhanced participants’ capacities in project planning, design, implementation, and management, while fostering critical thinking and problem-solving skills by adopting transdisciplinary approaches. Furthermore, participants demonstrated improved leadership, project management, time management, and communication skills. The training helped YWPs to equip them with a holistic perspective and stakeholder-focused mindset to address diverse water challenges from a holistic and long-term standpoint

Modelling the loss of nitrification inhibitor dosed in water distribution systems subject to pipe corrosion

Copper sulphate dosed as a nitrifier inhibitor in water distribution systems has encountered dramatic loss due to iron pipe corrosion. Chosen as the representative of iron corrosion products, ferric hydroxide flocs at low concentration (<2mg/L) bulk water was found capable of removing dissolved copper via adsorption obeying Freundlich isotherm equation. The adsorption rate can be predicted using a modified Pseudo2second order equation. These two adsorption equations enabled the possibility of modelling dissolved copper loss in the field pipeline caused by iron corrosion. With a few reasonable hydraulic assumptions and corrosion patterns made, the established model succeeded in simulating copper loss occurring in the pipeline where copper dosing has been exercised. These findings and the model established shed light on identifying and quantifying the copper loss mechanism in the field and provide modelling tools to improve the nitrifier inhibition strategy for the long term protection of chloramine in the water distribution system

Nitrification control by adjusting pH in severely nitrified bulkwaters

Nitrification control is complicated and expensive, especially when nitrification has reached aseverely nitrifying stage. Under this condition, utilities usually apply re-chloramination with limitedsuccess. Adjusting pH may benefit utilities. However, it is not clear whether pH should be moved upor down, and pH adjustment will also alter the chloramine decay profile (biocide) and ammonia (food)concentration. It is important to understand how this behaviour will ultimately impact nitrifyingbacterial activity. We collected samples from severely nitrifying bulkwaters and adjusted the pHwithin a practical range to know which pH benefits the most. Results showed that even a slightincrease in pH can help in protecting the chloramine residual and suppressing nitrifying bacterialactivity

Effect of temperature on onset of nitrification in chloraminated distribution system

Controlling nitrification is a challenge as the causes of onset of severe nitrification in chloraminated distribution systems are not yet well identified. Biostability concept is recently introduced to define the conditions at which nitrification would onset. At biostable residual, growth rate is balanced by disinfection rate. Growth rate is a function of free ammonia present, maximum growth rate, and coefficients defining the balance are assumed constant. Although maximum growth rate and disinfection rate coefficients are known to vary with temperature, it is yet to be taken into account. Water temperature in distribution systems varies between 6 and 35°C. Optimum temperature for ammonia oxidising bacteria (AOB) is between 25 and 30°C, which makes the variation of growth rate non-exponential beyond 20°C. In this paper, how biostability curve would alter within the full practical range of practical temperature is shown, by analysing the data obtained for a bacterium that behaves similar to AOB found in distribution systems

Chlorine decay prediction in bulk water using the parallel second order model: An analytical solution development

All distributed drinking water receives some form of disinfection and a minimum disinfectant residual should be maintained at the customer tap. The most popular disinfectant is chlorine. Chlorine reacts with compounds in water and hence decays. Description of chlorine decay is often difficult, due to a complex set of reactions and an initial fast reaction followed by a slower reaction. Before any attempt could be made to understand the decay characteristics in the distribution system, chlorine decay in bulk water has to be correctly described. The parallel second order reaction model was found to be one of the most suitable models for this purpose. However, widespread use of this model is hindered by its complexity, most importantly the non-existence of an analytical solution. In this paper, an analytical solution for this model was developed by initially assuming that the ratio (α) of slow and fast reaction rate coefficients is small. The estimated parameters and the chlorine residuals predicted by the numerical analysis and the proposed solution were compared for the chlorine decay data sets obtained from the literature as well as laboratory analysis. The results showed that the proposed analytical solution was very accurate for the prediction of chlorine decay behaviour in all samples

Major mechanism(s) of chloramine decay in rechloraminated laboratory scale system waters

Traditionally it is believed that nitrification was solely responsible for the widely observed chloramine loss under nitrifying conditions. On the contrary, recent results have shown that an unidentified agent (soluble microbial products or modified natural organic matter) chemically accelerates chloramine decay in rechloraminated nitrifying samples which were filtered to eliminate microbes. However, how those agents accelerate chloramine decay is not known. Mildly and severely nitrified samples were collected from a laboratory scale system and microbes were separated through filtration and then rechloraminated. To understand the mechanism, simple stoichiometry was employed. In all samples, rechloramination induced ammonia loss possibly by auto-decomposition, especially in the initial stages. In severely nitrified samples, accelerated auto-decomposition and nitrite oxidation were found to be the major mechanisms chemically accelerating the chloramine loss indicating that the agent did not demand appreciable chloramine. However, in the mildly nitrified water, a large discrepancy in chloramine demand what is explainable by stoichiomatye was seen. The natural organic matter (NOM) oxidation was suspected to be the dominant mechanism during the prolonged incubation of mildly nitrified samples. The identification of the agent is important as it highly accelerates chloramine decay

Optimal temperature for microbes in an acetate fed microbial electrolysis cell (MEC)

Temperature is one of the important parameters which can significantly effect on the activity/selection of microorganism and subsequently on the reactor's performance. Two microbial electrolysis cells (MECs) were operated at different temperature settings with acetate as a carbon source. On average, COD removal rates of 16.8, 24.7, 34.0, 36.2 and 18.1mg/l/h were recorded at 25, 29, 30, 31 and 35°C, respectively. The results of volatile suspended solids analysis indicated that biomass concentration continued to drop at all temperatures, but the drop was the lowest at 30°C. Consideration of biomass drop and specific COD removal rate showed 31°C as the optimum temperature. These significant results imply that effect of temperature and change in biomass concentration should be considered in future experiments when expressing the removal rates

Effect of silver in severely nitrified chloraminated bulk waters

Chloramine has been widely used in many water utilities as a secondary disinfectant because of increased concern over disinfection by-products (DBPs) formation. However, its popularity has been affected due to microbial acceleration, which is traditionally believed to be by nitrifying organisms or their products such as nitrite and pH value which change substantially under nitrifying conditions. With the traditional belief in mind, the conventional approach to solve 'chloramine decay' was aimed at killing or flushing out nitrifiers. We have recently shown that either soluble microbial products (SMPs) released by microbes or changes in natural organic matter (NOM) characteristics under nitrified conditions could be responsible for the acceleration. With this new insight, a new control strategy was attempted by dosing silver at a concentration of 0.1 mg-Ag/L to the nitrified bulk waters obtained in a laboratory scale system. Accelerated chemical and microbial chloramine losses were significantly reduced after the addition of silver. These results are very promising for future applications

Importance of the order in enhancing EfOM removal by combination of BAC and MIEX®

Biological activated carbon (BAC) is operationally a simple treatment which can be employed to remove effluent organic matter (EfOM) from secondary wastewater effluent (SWWE). Unfortunately, BAC removes only a limited amount of dissolved organic carbon (DOC). Thus, maximizing DOC removal from SWWE using BAC is a major concern in wastewater reuse. This study has investigated a hybrid system of BAC and Magnetic Ion Exchange Resin (MIEX®) for the enhanced removal of DOC. Performance of both BAC prior to MIEX® (BAC/MIEX®) and reverse (MIEX®/BAC) combination was evaluated in terms of DOC removal. The BAC/MIEX® showed much better DOC removal. This is because microbial activity in the BAC bed converted MIEX® non-amenable DOC to MIEX® amenable DOC. As a result, BAC/MIEX® combination synergised DOC removal. In addition, BAC was also found to be highly effective in reducing MIEX® dose for a given DOC removal from SWWE