Panagiotis Elefsiniotis

Corrosion control in water supply systems: Effect of pH, alkalinity, and orthophosphate on lead and copper leaching from brass plumbing

This study explored the potential of lead and copper leaching from brass plumbing in the Auckland region of New Zealand. A five-month field investigation, at six representative locations, indicated that Aucklands water can be characterized as soft and potentially corrosive, having low alkalinity and hardness levels and a moderately alkaline pH. More than 90% of the unflushed samples contained lead above the maximum acceptable value (MAV) of 10 μg/L (New Zealand Standards). In contrast, the copper level of unflushed samples remained consistently below the corresponding MAV of 2 mg/L. Flushing however reduced sharply metal concentrations, with lead values well below the MAV limit. Generally, metal leaching patterns showed a limited degree of correlation with the variations in temperature, dissolved oxygen and free chlorine residual at all sampling locations. Furthermore, a series of bench-scale experiments was conducted to evaluate the effectiveness of pH and alkalinity adjustment, as well as orthophosphate addition as corrosion control tools regarding lead and copper dissolution. Results demonstrated that lead and copper leaching was predominant during the first 24 hr of stagnation, but reached an equilibrium state afterwards. Since the soluble fraction of both metals was small (12% for lead, 29% for copper), it is apparent that the non-soluble compounds play a predominant role in the dissolution process. The degree of leaching however was largely affected by the variations in pH and alkalinity. At pH around neutrality, an increase in alkalinity promoted metal dissolution, while at pH 9.0 the effect of alkalinity on leaching was marginal. Lastly, addition of orthophosphate as a corrosion inhibitor was more effective at pH 7.5 or higher, resulting in approximately 70% reduction in both lead and copper concentrations.

Effect of mixture ratio, solids concentration and hydraulic retention time on the anaerobic digestion of the organic fraction of municipal solid waste.

This paper describes how the degradation of the organic fraction of municipal solid waste (OFMSW) is affected through codigestion with varying amounts of return activated sludge (RAS). Solid waste that had its inorganic fraction selectively removed was mixed with RAS in ratios of 100% OFMSW, 50% OFMSW/50% RAS, and 25% OFMSW/75% RAS. The total solids (TS) concentration was held at 8% and three anaerobic digester systems treating the mixtures were held (for the first run) at a total hydraulic retention time (HRT) of 28 days. Increasing amounts of RAS did not however improve the mixture’s digestability, as indicated by little change and/or a drop in the main performance indices [including percentage volatile solids (VS) removal and specific gas production]. The optimum ratio in this research therefore appeared to be 100% OFMSW with an associated 85.1 ± 0.6% VS removal and 0.72 ± 0.01 L total gas g- 1 VS. In the second run, the effect of increasing percentage of TS (8, 12% and 15%) at a system HRT of 28 days was observed to yield no improvement in the main performance indices (i.e. percentage VS removal and specific gas production). Finally, during the third run, variations in the total system HRT were investigated at an 8% TS, again using 100% OFMSW. Of the HRTs explored (23, 28 and 33 days), the longest HRT yielded the best performance overall, particularly in terms of specific gas production (0.77 ± 0.01 L total gas g-1 VS).

Biodegradation behavior of agricultural pesticides in anaerobic batch reactors

This study explored the biodegradation potential of two agricultural pesticides (2,4-D and isoproturon) as well as their effect on the performance of the anaerobic digestion process. Three 3.5 L batch reactors were used, having the same initial isoproturon concentration (25 mg/L) and different 2,4-D concentrations (i.e. 0, 100, or 300 mg/L, respectively). All systems were fed with equal amounts of primary sludge and digested sludge and operated at the low mesophilic range (32 ± 2°C). Following an acclimation period of approximately 30 days, complete 2,4-D removal was achieved, whereas isoproturon biodegradation was practically negligible. The presence of 2,4-D did not have a direct effect on acidogenesis since soluble organic carbon [expressed either as volatile fatty acids (VFAs) or as total organic carbon (TOC)] peaked within the first 10 days of operation in all bioreactors. Utilization of VFAs however appeared to follow two distinct patterns: one pattern was represented by acetate and butyrate (i.e. no acid accumulation) while the other was followed by propionate, isobuturate, valerate and isovalerate (i.e. acid accumulation, duration of which was related to the initial 2,4-D concentration). On the whole, all reactors exhibited a successful digestion performance demonstrated by complete VFAs utilization, considerable gas production (containing 45 to 65% methane by volume), substantial volatile suspended solids (VSS) reduction (42 to 50%), as well as pH and alkalinity recovery.

Two-phase anaerobic digestion of the organic fraction of municipal solid waste: estimation of methane production

Energy generation from methane (CH4) is one of the primary targets of the anaerobic digestion process. Consequently, the focus of this study was to investigate the effect on CH4 production of total solids (TS) loading (measured as % TS) and hydraulic residence time (HRT) during the treatment of the organic fraction of municipal solid waste (OFMSW). Laboratory-scale, two-phase anaerobic digestion systems were employed with each system consisting of an acidogenic reactor and a methanogenic reactor linked in series. The group A runs in the experiment explored the effect on digester performance of four variations in methanogenic HRT (15, 20, 25 and 30 days) at three different feed TS concentrations (8, 12 and 15%). The group B runs compared the actual methane yield (0.14 to 0.45 L g VS feed − 1 ) to that predicted by the Chen–Hashimoto model. Results from the group A runs indicated that acidogenesis improved with an increase in % TS and a decrease in HRT; while, methanogenesis behaved inversely, achieving higher yields at the lower % TS and longer HRT values. In comparison with the group B runs, the Chen–Hashimoto model under-predicted (by an average of 16.5 ± 6.6%) the CH4 yield obtained from the digestion of OFMSW.

TREATMENT OF FOUR INDUSTRIAL WASTEWATERS BY SEQUENCING BATCH REACTORS : EVALUATION OF COD, TKN AND TP REMOVAL

Abstract This study investigated the ability of a sequencing batch reactor (SBR) system to treat four industrial wastewaters, namely, textile, landfill leachate, seafood and slaughterhouse effluents. The system employed three identical SBRs (10 l volume each) operating in parallel and each waste was treated one at a time. The operational variables examined included the length of the non‐aerated period and the solids retention time (SRT). All four wastewaters experienced chemical oxyfen demand (COD) and total kjeldhal nitrogen (TKN) removals greater than 81%, while the TP removals were lower, ranging from 57 to 94%. The length of the non‐aerated period appeared to have minimal effect on the SBR performance; however, increases in SRT reduced the percent TP removal for the textile and leachate wastes only. In addition, to investigate organic loading limits to the seafood SBR system, the COD was increased by three increments of 250 mg l−1 starting from a baseline concentration of 1100 mg l−1. This resulted in a reduction in both the TKN and TP removal at the higher concentrations. Finally, for the slaughterhouse wastewater, the COD:TKN ratio was tested at levels of 6:1, 8:1 and 9:1 with the result that only the TP removal was affected at the lowest ratio.

Treatment of a slaughterhouse wastewater: effect of internal recycle rate on chemical oxygen demand, total Kjeldahl nitrogen and total phosphorus removal

This study investigated the ability of an anaerobic/anoxic/oxic (A2/O) system to treat a slaughterhouse wastewater. The system employed two identical continuous-flow reactors (10 l total liquid volume each) running in parallel with the main operational variable, being the internal recycle (IR) rate. The chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) performance was evaluated as the IR flowrate was increased from a Q of 15 l d−1 to 4Q at a system hydraulic retention time of 16 h and a solids retention time of 10 d. The COD:TKN and COD:TP ratios were 8.2:1 and 54:1, which supported both nitrogen and phosphorus removal. For all IR multiples of Q, the COD removal was in excess of 90%. The TKN removal showed a modest improvement (a 4–5% increase, depending on the dissolved oxygen (DO)) as the IR doubled from Q to 2Q, but no further increase was observed at the 4Q IR rate. The TP removal reached its optimum (around 85%–89% (again depending on the DO)) at the 2Q rate.

The influence of organic loading and anoxic/oxic times on the removal of carbon, nitrogen and phosphorus from a wastewater treated in a sequencing batch reactor

In this study, 10 L sequencing batch reactors (SBRs) were operated at a 12-h cycle length (four alternating anoxic/oxic conditions) to assess the biological nutrient removal potential of a domestic wastewater treated at the Huay Kwang plant, Bangkok, Thailand. The wastewater was found to be carbon-limited (chemical oxygen demand (COD) to total Kjeldahl nitrogen (TKN) (i.e., COD:TKN) ratio of 6.4:1). This ratio was insufficient to support good phosphorus removal. Glucose was therefore added to increase the COD:TKN ratio ultimately to 10:1 and the COD, TKN and total phosphorus (TP) removals at this ratio were all in excess of 95%. An alternative carbon source from a local fruit canning industry was then added at the same COD:TKN ratio; and, in order to increase the throughput of the waste treated, the cycle length was simultaneously shortened to 8 h keeping approximately the same anoxic/oxic fractions. The COD removal remained high (> 95%), however the TKN and TP removals were substantially reduced (79% and 66%, respectively), indicating that the shortened cycle length was sub-optimum. The last phase of the research involved changing the anoxic/oxic fractions of the cycle time to maximize performance. It was found that for the conditions studied in this research, the performance improved in proportion to the increase in the first anoxic fraction, being most stable at the highest anoxic fraction of the cycle length (0.33).

The effect of upper mesophilic temperature and feed-to-seed ratio on batch anaerobic digestion systems

This study investigated the effect of upper mesophilic temperature and feed-to-seed (F/S) ratio on anaerobic digestion using four 3.5 L batch-scale reactors. Initially, eight F/S ratios, ranging from 10/90 to 90/10, were explored at 37°C, using a mixture of primary and secondary municipal sludge as feed. It was observed that the systems with low F/S ratios (40/60 and below) showed a stable performance while those with high ratios (50/50 and above) experienced the effect of organic overloading indicated by reduced removal of volatile solids (VS) in the feed, a drop in pH, volatile fatty acid (VFA) accumulation during the first 10 days of operation, and total gas production markedly lower than the corresponding theoretical values. Subsequently, the effect of temperature, in the 37 to 49°C range, was studied at an F/S ratio of 20/80. Results revealed that an increase in temperature between 37 and 43°C had a rather minimal effect on the process, with the exception of a moderate increase in total gas production. A further rise in the temperature in the 45 to 49°C range however appeared to trigger an adverse effect evidenced by enhanced percent VSS reduction (possibly the result of cell lysis), VFA accumulation and an increase in the non-VFA total organic carbon (TOC) content. Therefore, it can be concluded that an operating temperature in the 37 to 43°C range resulted in a stable and satisfactory reactor performance.

Biodegradation of industrial-strength 2,4-dichlorophenoxyacetic acid wastewaters in the presence of glucose in aerobic and anaerobic sequencing batch reactors

This research explored the biodegradability of 2,4-dichlorophenoxyacetic acid (2,4-D) in two laboratory-scale sequencing batch reactors (SBRs) that operated under aerobic and anaerobic conditions. The potential limit of 2,4-D degradation was investigated at a hydraulic retention time of 48 h, using glucose as a supplemental substrate and increasing feed concentrations of 2,4-D; namely 100 to 700 mg/L (i.e. industrial strength) for the aerobic system and 100 to 300 mg/L for the anaerobic SBR. The results revealed that 100 mg/L of 2,4-D was completely degraded following an acclimation period of 29 d (aerobic SBR) and 70 d (anaerobic SBR). The aerobic system achieved total 2,4-D removal at feed concentrations up to 600 mg/L which appeared to be a practical limit, since a further increase to 700 mg/L impaired glucose degradation while 2,4-D biodegradation was non-existent. In all cases, glucose was consumed before the onset of 2,4-D degradation. In the anaerobic SBR, 2,4-D degradation was limited to 120 mg/L.

Treatment of a Textile Dye Wastewater by an Electrochemical Process

This study explored the effectiveness of an electrochemical process to treat a sulfur dye wastewater from a textile industry. The treatment system included a 4.0 L reactor equipped with five steel electrode plates, and a separate sedimentation tank of equal liquid volume. The experimental part involved two distinct, sequential stages. In the first stage, the effect of initial pH and electrical charge (i.e., current times reaction time) on the treatment process was explored. Experiments were conducted in a factorial mode, involving three initial pH values (3, 4 and 5), and six electrical charges (ranging from 150 to 1,350 coulomb), respectively. Results indicated that chemical oxygen demand (COD), total suspended solids (TSS), and color removal efficiency improved with a decrease in initial pH and an increase in electrical charge. Overall, high percent removal values were observed ranging from 63% to 80% for COD, 81% to 96% for TSS, and 93% to 99% for color. During the second stage, the electrode corrosion pattern was investigated for a period of 45 days. Under stable operating conditions, electrode consumption was found to conform to Faradays law. Moreover, process performance regarding COD, TSS, and color reduction was comparable to that obtained in the first stage of the study.