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

An integrated kinetic model for organic and nutrient removal by duckweed-based wastewater treatment (DUBWAT) system

This study was conducted to investigate the efficiency of duckweed (Lemna gibba) in treating a domestic wastewater and to develop an integrated kinetic model for organic and nutrient removal by duckweed-based wastewater treatment (DUBWAT) system. Four pilot-scale DUBWAT units, made of concrete blocks, were operated under ambient conditions (temperatures 30-36 °C), different hydraulic retention times (t), organic loading rates (OLR) and stocking densities (SD). The maximum COD, BOD5, NH3-N, TN and TSS removal efficiencies of 84, 88, 68, 58 and 87%, respectively, were found at optimum operating conditions of t of 10 days, OLR of 50 kgCOD/(ha-d) and SD of 0.5 kg/m2. The nitrogen uptake rate by duckweed was found to be 0.62 g-N/(m2-d). An integrated kinetic model consisting of t, OLR, SD and temperature was developed for the DUBWAT system and validated satisfactorily with data obtained from the literatures

Comparative study of ground water treatment plants sludges to remove phosphorous from wastewater

Alum- and iron-based sludge obtained from water treatment plant produced during a unit treatment process (coagulation and flocculation) have been widely tested as a low-cost adsorbent to remove phosphorous (P) from wastewater. However, the effectiveness of iron-based sludge generated from the oxidation of iron which naturally occurs in the ground water has not been investigated. Moreover, influences of dominant metals ions comprised in the treatment plants sludges on P adsorption capacity and rate from wastewater are not yet known. This study, therefore, employed four different groundwater treatment plants sludges iron-based (from the oxidation of iron) and alum-based (from coagulation and flocculation process) to determine their P adsorption capacities and adsorption rates from the synthetic wastewater (SWW) and secondary effluent wastewater (SEWW). Although metals ions concentrations were the highest in the iron-based sludge amongst the sludge used in this study, it appeared to have the lowest P adsorption capacity and adsorption rate. A good correlation between aluminium to iron mass ratio and adsorption capacity for both types of waters were noted. However, a poor relation between aluminium to iron mass ratio and adsorption rates for the SEWW was observed. Further, the tested sludges were found to have a better P removal efficiency and adsorption capacity from the SEWW than from the SWW. Thus, this study demonstrates the ground water treatment plants sludges could be a low cost and effective adsorbent in removing P from wastewater

Influence of treatment processes and disinfectants on bacterial community compositions and opportunistic pathogens in a full-scale recycled water distribution system

In this study, for the first time, a recycled water distribution system was analysed in which the inorganic nitrogen content in the recycled water was substantially minimised (85%) having minimal disinfection abilities. The majority of the bacterial communities were proteobacteria comprising alpha-, beta-, and gamma-proteobacteria, similar to the drinking water distribution system. The gene copy numbers of total bacterial 16S ribosomal ribonucleic acid (16S rRNA) and opportunistic pathogens (OPs) were significantly decreased after the chlorination, but their populations increased with the decrease of total chlorine residual level in the distribution system. The total bacterial 16S rRNA significantly correlated with Legionella spp., Mycobacterium spp., and Pseudomonas aeruginosa. Similarly, significant correlations existed between OPs (particularly Legionella spp. and Pseudomonas aeruginosa) and iron-oxidising, manganese-oxidising, and sulphate-reducing bacterial genera. The detection of several OPs in the absence of E. coli shows that the traditional indicator used for compliance monitoring may not accurately represent the microbial water quality. This study suggests monochloramine as an alternative secondary disinfectant

Does the onset of nitrification equally impact in decaying chloramine?

Accelerated chloramine decay is normally observed after the onset of nitrification in the chloraminated water distribution systems. However, it is unknown whether the onset of nitrification equally impacts in decaying chloramine in different water distribution systems. To compare the impact of nitrification on chloramine decay, bulk water samples collected from the three distribution systems were tested. After the onset of nitrification, different chloramine decay rates were observed. Total decay coefficients of chloramine increased by 4–10 times in the samples obtained from Sydney Water Distribution System (SWDS) and lab-scale system whereas the decay rates increased by only 3–3.5 times in the samples obtained from Goldfields and Agricultural Water Supply System (GAWSS) after the onset of nitrification. The chloramine decay rate increased with ammonia drop rate, but the other mechanisms could not be ruled out. If chloramine residuals have to be controlled not only nitrification but also other mechanisms should be understood and controlled

Is nitrite from nitrification the only cause of microbiologically induced chloramine decay?

Nitrite, produced by ammonia oxidizing bacteria (AOB), was traditionally thought to be the only cause of microbiologically mediated decay of chloramine. The development and application of microbial decay factor method and bacterial community studies, for the first time have revealed many other factors such as soluble microbial products (SMPs) and bacteria other than AOB mediating the decay of chloramine

An assessment of the persistence of putative pathogenic bacteria in chloraminated water distribution systems

This study investigated how a chloramine loss and nitrifying conditions influenced putative pathogenic bacterial diversity in bulk water and biofilm of a laboratory- and a full-scale chloraminated water distribution systems. Fifty-four reference databases containing full-length 16S rRNA gene sequences obtained from the National Centre for Biotechnology Information database were prepared to represent fifty-four pathogenic bacterial species listed in the World Health Organisation and Australian Drinking Water Quality Guidelines. When 16S rRNA gene sequences of all samples were screened against the fifty-four reference pathogenic databases, a total of thirty-one putative pathogenic bacteria were detected in both laboratory- and full-scale systems where total chlorine residuals ranged between 0.03 - 2.2 mg/L. Pathogenic bacterial species Mycolicibacterium fortuitum and Pseudomonas aeruginosa were noted in all laboratory (i.e. in bulk water and biofilm) and in bulk water of full-scale samples and Mycolicibacterium fortuitum dominated when chloramine residuals were high. Other different pathogenic bacterial species were observed dominant with decaying chloramine residuals. This study for the first time reports the diverse abundance of putative pathogenic bacteria resilient towards chloramine and highlights that metagenomics surveillance of drinking water can serve as a rapid assessment and an early warning of outbreaks of a large number of putative pathogenic bacteria

Investigation on laboratory and pilot-scale airlift sulfide oxidation reactor under varying sulfide loading rate

Airlift bioreactor was established for recovering sulfur from synthetic sulfide wastewater under controlled dissolved oxygen condition. The maximum recovered sulfur was 14.49 g/day when sulfide loading rate, dissolved oxygen (DO) and pH values were 2.97 kgHS-/m3-day, 0.2-1.0 mg/L and 7.2-7.8, respectively. On the other hand, the increase in recovered sulfur reduced the contact surface of sulfide oxidizing bacteria which affects the recovery process. This effect caused to reduce the conversion of sulfide to sulfur. More recovered sulfur was produced at high sulfide loading rate due to the change of metabolic pathway of sulfide-oxidizing bacteria which prevented the toxicity of sulfide in the culture. The maximum activity in this system was recorded to be about 3.28 kgS/kgVSS-day. The recovered sulfur contained organic compounds which were confirmed by the results from XRD and CHN analyzer. Afterwards, by annealing the recovered sulfur at 120°C for 24 hrs under ambient Argon, the percentage of carbon reduced from 4.44% to 0.30%. Furthermore, the percentage of nitrogen and hydrogen decreased from 0.79% and 0.48% to 0.00% and 0.14%, respectively. This result showed the success in increasing the purity of recovered sulfur by using the annealing technique. The pilot-scale biological sulfide oxidation process was carried out using real wastewater from Thai Rayon Industry in Thailand. The airlift reactor successfully removed sulfide more than 90% of the influent sulfide at DO concentration of less than 0.1 mg/L, whereas the elementary sulfur production was 2.37 kgS/m3-day at sulfide loading rate of 2.14 kgHS-/m3-day. The sulfur production was still increasing as the reactor had not yet reached its maximum sulfide loading rate

Effectiveness of devices to monitor biofouling and metals deposition on plumbing materials exposed to a full-scale drinking water distribution system

A Modified Robbins Device (MRD) was installed in a full-scale water distribution system to investigate biofouling and metal depositions on concrete, high-density polyethylene (HDPE) and stainless steel surfaces. Bulk water monitoring and a KIWA monitor (with glass media) were used to offline monitor biofilm development on pipe wall surfaces. Results indicated that adenosine triphosphate (ATP) and metal concentrations on coupons increased with time. However, bacterial diversities decreased. There was a positive correlation between increase of ATP and metal deposition on pipe surfaces of stainless steel and HDPE and no correlation was observed on concrete and glass surfaces. The shared bacterial diversity between bulk water and MRD was less than 20% and the diversity shared between the MRD and KIWA monitor was only 10%. The bacterial diversity on biofilm of plumbing material of MRD however, did not show a significant difference suggesting a lack of influence from plumbing material during early stage of biofilm development

Potential of biologically activated carbon to improve chlorine stability from biodegradation in surface waters

We report that biological activated carbon (BAC) has the significant potential to improve chlorine stability in the drinking water and dissolved organic carbon (DOC) is not a good indicator of chlorine stability. The BAC followed by enhanced coagulation (EC) could be beneficial for improving chlorine stability. BAC granules obtained from an aged (>26,000-bed volume over a year) BAC column was incubated in the same surface water. The prolonged (58 days) incubation achieved a DOC removal (up to 47%) and improvement of chlorine stability (up to 93% of chlorine reactive agents) with time. Surprisingly, a smaller initial biological removal in DOC (12% or 0.61 mg/L) by BAC substantially improved chlorine stability (64% of chlorine reactive agents), but a further improvement per mg-DOC removal is small. BAC process removes non-coagulable compounds that are chlorine reactive, but at the same time increases the coagulable compounds that are chlorine reactive, implying coagulation after BAC (BAC/EC) is beneficial in stabilising the chlorine and DOC removal. Over the incubation period, a shift in the microbial community is less significant except for the abundance of Nitrospira increasing with the removal in biodegradable organic carbon. BAC treatment followed by coagulation is a good strategy, but the evaluation should be based on chlorine stability and disinfection by-products (DBPs) formation rather than the DOC