Magnetite nanoparticles can boost methane production via direct interspecies electron transfer. However, the combined effect of inoculum and particle characteristics on magnetite's methanogenesis stimulation is poorly understood. Here, the influence of inoculum type, particle size, and particle concentration on the ability of magnetite to accelerate methanogenesis was studied in batch anaerobic digestion experiments. Fresh and degassed mesophilic digester sludge was used as inoculum, representing methanogenic communities in the exponential or stationary growth and endogenous decay phases, respectively. Three magnetite particle size ranges, small (50–150 nm), medium (168–490 nm), and large (800 nm–4.5 μm), at two different concentrations (2 and 7 mM) were used. With degassed sludge, the effect of magnetite on the methane production rate was weak and depended on the particle size and concentration. Only magnetite of medium size at both 2 and 7 mM significantly increased the methane production rate by 12% compared to the control with no magnetite. The lag phase was reduced by 17% compared to the control, only with 2 mM of both small and medium size magnetite. Conversely, adding magnetite into fresh sludge significantly increased the methane production rate by an average of 32% while simultaneously decreasing the lag phase by 15%–40%, as compared to the control, independently of the magnetite's size and concentration. The stimulation of methane production depends on magnetite and inoculum characteristics.

 Abstract — Anaerobic batch experiments were conducted to investigate the effect of magnetite-supplementation (7 mM) on methane production from digested sludge undergoing two different microbial growth phases, namely fresh sludge (exponential growth phase) and degassed sludge (endogenous decay phase). Three different particle sizes were assessed: small (50 - 150 nm), medium (168 – 490 nm) and large (800 nm - 4.5 µm) particles. Results show that, in the case of the fresh sludge, magnetite significantly enhanced the methane production rate (up to 32%) and reduced the lag phase (by 15% - 41%) as compared to the control, regardless of the particle size used. However, the cumulative methane produced at the end of the incubation was comparable in all treatment and control bottles. In the case of the degassed sludge, only the medium-sized magnetite particles increased significantly the methane production rate (12% higher) as compared to the control. Small and large particles had little effect on the methane production rate but did result in an extended lag phase which led to significantly lower cumulative methane production at the end of the incubation period. These results suggest that magnetite produces a clear and positive effect on methane production only when an active and balanced microbial community is present in the anaerobic digester. It is concluded that, (i) the effect of magnetite particle size on increasing the methane production rate and reducing lag phase duration is strongly influenced by the initial metabolic state of the microbial consortium, and (ii) the particle size would positively affect the methane production if it is provided within the nanometer size range.

This research investigated the potential for industrial-strength 2-methyl-4-chlorophenoxyacetic acid (MCPA) degradation by activated sludge microorganisms in a sequencing batch reactor (SBR) under nitrate-reducing conditions. The research was divided into four phases consisting of Phase I (a "proof-of-concept" phase); Phase II (an initial "tolerance" exploration phase); Phase III (an "effect of hydraulic retention time" phase), and Phase IV (a "limits" phase). The SBR successfully and simultaneously removed the nitrates completely and around 98 % of the MCPA up to an initial concentration of 50 mg/L MCPA in the dimethylamine salt form (DMCPA) (Phases I, II and III); however, it took approximately 28 days to observe a steady, high-level of MCPA removal. When the concentration of DMCPA was increased to 75 mg/L (Phase IV), the MCPA removal efficiency dropped to 85 %, but removal was observed only for a relatively short period of time since the biomass appeared to eventually become saturated with the herbicide, stopping conversion of DMCPA to its acid form and halting biodegradation.

This paper compares the practical limits of 2, 4-dichlorophenoxy acetic acid (2,4-D) degradation that can be obtained in two laboratory-scale anaerobic digestion systems; namely, a sequencing batch reactor (SBR) and a single-fed batch reactor (SFBR) system. The comparison involved synthesizing a decade of research conducted by the lead author and drawing summative conclusions about the ability of each system to accommodate industrial-strength concentrations of 2,4-D. In the main, 2 L liquid volume anaerobic SBRs were used with glucose as a supplemental carbon source for both acid-phase and two-phase conditions. Volatile fatty acids however were used as a supplemental carbon source for the methanogenic SBRs. The anaerobic SBRs were operated at an hydraulic retention time of 48 hours, while being subjected to increasing concentrations of 2,4-D. The SBRs were able to degrade between 130 and 180 mg/L of 2,4-D depending upon whether they were operated in the acid-phase or two-phase regime. The methanogenic-only phase did not achieve 2,4-D degradation however this was primarily attributed to difficulties with obtaining a sufficiently long SRT. For the two-phase SFBR system, 3.5 L liquid-volume digesters were used and no difficulty was experienced with degrading 100 % of the 2,4-D concentration applied (300 mg/L).

In this research, loess addition was investigated as a possible means of controlling the bulking sludge generated from a sequencing batch reactor (SBR) system treating a synthetic wastewater. The specific objective was to investigate whether loess changed the morphology of the sludge (i.e., influenced the relative abundance of filamentous species), as opposed to improving settling simply because the clay portion of the loess acted as a flocculating agent. To this end, two sets of batch tests were performed using 1 L reactors filled with bulking sludge from the SBR. The first set of batch tests investigated the effect of different loess concentration on the settling properties of the sludge; thus loess was added in concentrations of 0.0, 0.4, 2.0 and 5.0 g L−1. The 5.0 g L−1 loess concentration exhibited the most positive results on settling, bringing the modified sludge volume index (SVI) down into the target range of 150 mL g−1. The second set of batch tests investigated filament length along with the modified SVI. It appeared that at the microbial level, 5.0 g L−1of loess caused no reduction in filament length, suggesting no reduction in the amount of filamentous microorganisms. This means that adding loess to a system after it has bulked has the potential to mask the bulking problem by improving settling, while not fixing the problem microbiologically.

"Environmental Ethics and Sustainability: A Casebook for Environmental Professionals." Civil Engineering and Environmental Systems, 31(4), pp. 367–368

This research assesses the potential for co-treatment of a dairy wastewater with a domestic wastewater in a lab-scale, continuous-flow, activated sludge system. To evaluate the influence of the dairy waste contribution, seven runs were conducted with each run being a mixture of dairy wastewater (either cheese or milk) in different ratios ranging from 1:0.01 to 1:0.30 by volume. More than 87% of the carbon was removed for both waste additions; however, while 95% ammonia-nitrogen removal was recorded for the cheese waste, only 75% removal was obtained for the milk. Kinetic studies for carbon consumption revealed a first-order model with lower kinetic constants as the cheese waste proportion increased. Specific carbon consumption rates indicated that the biomass had not reached its maximum potential to degrade carbon. The ability of the biomass to settle was hindered when the Gram negative to Gram positive filamentous bacteria ratio increased to approximately 1.5.

New Zealand Ironsand (NZIS), an iron-rich sand ubiquitous to the coast of the North Island of New Zealand was examined for the removal of arsenic (both As (III) and As (V)) by adsorption. Batch experiments were performed to evaluate the adsorption kinetics at three different pH conditions (3.0, 7.5 and 11.0). In addition, a column test was conducted to obtain the breakthrough curve and appraise the arsenic removal capacity of NZIS used as a filter media. The kinetic study showed that a very long contact time (>144 h) was needed to reach equilibrium and the nature of the adsorption was well described (R2 value more than 0.96 at each pH condition) with a pseudo–second-order adsorption kinetic model for both As (III) and As (V). In column tests, a pore volume (PV) of 700 and 400 yielded a total arsenic level less than the WHO guideline value of 10 μg/L for As (III) and As (V), respectively.

Pacific Island countries rely heavily on imported, expensive and unsustainable fossil fuels as their primary source for energy production. Establishing an alternative energy source from local resources would have considerable benefits; thus, the purpose of this research was to investigate the biogas generation potential of coconut copra during anaerobic digestion. Both batch and semi-continuous stirred tank reactors (SCSTRs) were investigated to optimise methane (CH 4 ) production and increase overall conversion efficiency. The results suggest that coconut copra is amenable to anaerobic digestion with high theoretical methane yields available from the substrate’s high lipid content. However, the optimal organic loading (OL) was limited to within a narrow range of 3·6–6·0 g volatile solids (VS) (2·4–4·0 g VS/L reactor) for the batch reactors. A maximum of 0·420 L CH 4 /g VS was achieved at an OL of 3·6 g VS. High average methane yields of 0·708 L CH 4 /g VS·day were also successfully achieved for the SCSTRs, whereas increased mixing improved methane production.

The coffee agro-industry generates a large volume of wastewater that is notable for its high organic strength as well as its color content. Due to the seasonal nature of the harvest (3–4 months per year), this particular industrial waste needs a treatment method that is both reliable and fast (in terms of start-up time). As part of investigating a system capable of treating a coffee wastewater, this research evaluated four electrochemical advanced oxidation processes (EAOPs) using boron-doped diamond (BDD) electrodes. The processes were anodic oxidation (AO), anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF). Experimental conditions were as follows: 40 mA cm−2 current density (all EAOPs), 0.3 mmol Fe2+ L−1 (Fenton systems), 300 mL air min−1 (AO-H2O2, EF, PEF), and 500 μW cm−2 UV irradiation (photo-Fenton systems). The performance of the four EAOP treatment methods (in terms of color and organic carbon removal) was compared against two conventional chemical oxidation methods, namely, Fenton and photo-Fenton. The research indicated that the four EAOPs were better at removing color (89–93 %) and total organic carbon (TOC) (73–84 %) than the respective chemical Fenton (58 and 4.8 %) and photo-Fenton (61 and 7 %) methods. The trend in performance was as follows: AO-H2O2 > AO > PEF ≈ EF. It appeared that the ferrous iron reagent formed a dark-colored complex with some coffee components, diminishing the effect of Fenton reactions. In addition, the dark color of the wastewater limited the effect of light in the UV-Fenton processes. Analysis showed that acceptable levels of Fe2+ (0.3 mmol L−1) and energy (0.082–0.098 kWh g−1 TOC) were required by the EAOPs after 4-h treatment time. In conclusion, the use of electrochemical methods (equipped with BDD electrodes) seems a promising method for the effective treatment of coffee wastewaters.

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 48h, using glucose as a supplemental substrate and increasing feed concentrations of 2,4-D; namely 100 to 700mg/L (i.e. industrial strength) for the aerobic system and 100 to 300mg/L for the anaerobic SBR. The results revealed that 100mg/L of 2,4-D was completely degraded following an acclimation period of 29d (aerobic SBR) and 70d (anaerobic SBR). The aerobic system achieved total 2,4-D removal at feed concentrations up to 600mg/L which appeared to be a practical limit, since a further increase to 700mg/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 120mg/L.

High biomass productivity and efficient harvesting are currently recognized challenges in microbial biofuel applications. To produce naturally settleable biomass, combined growth of native microalgae and bacteria was facilitated in laboratory sequencing batch reactors (SBRs) using primary treated wastewater from the Christchurch Wastewater Treatment Plant (CWTP) in New Zealand. SBRs were operated under a simulated, local, summer climate (i.e., 925 mu mol/m(2)/s of photosynthetically active radiation for 14.7 h per day at 21 degrees C mean water temperature) using 1.4- to 8-day hydraulic retention times (HRTs) to optimize growth. Solids retention times (SRTs) were varied from 4 to 40 days by discharging different ratios of supernatant and completely mixed culture. Biomass productivity up to 31 g/m(2)/day of solids was obtained, and it generally increased as retention times decreased. Biomass settleability was typically 70-95%, and the microbes aggregated into compact flocs as cultures aged up to four months. Due to a low lipid content of 10.5%, anaerobic digestion appeared to be the most appropriate biofuel conversion process with potential to generate 19,200 m(3)/ha/yr of methane based on settleable mixture productivity. (C) 2012 Elsevier Ltd. All rights reserved.

This paper describes the impacts of the 2010–2011 Canterbury earthquakes on the city of Christchurch's liquid waste management system (i.e. the infrastructure associated with wastewater collection, treatment and disposal). The effect on each unit operation and process is documented along with the ‘state of progress’ of their repair. Significant problems arose because liquefaction caused massive amounts of silt to enter the sewerage network. This affected the next system in line by overloading the main solids-handling facilities of the wastewater treatment plant. One of the quakes (22 February 2011) also resulted in a loss of power to the plant with several downstream processes in the system failing because of the difficulty of foreseeing what would happen when power was restored. Observations are offered in respect to lessons learned from the disaster, and these include issues surrounding toilet deployment and the interaction between the various components of a city's liquid waste management system.

Energy generation from methane (CH(4)) is one of the primary targets of the anaerobic digestion process. Consequently, the focus of this study was to investigate the effect on CH(4) 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 VSfeed−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 CH(4) yield obtained from the digestion of OFMSW.

Adsorption is a technology used to remove arsenic from water contaminated at levels above drinking water standards. In this study, New Zealand Iron-Sand (NZIS), a naturally-available adsorbent was investigated for its efficiency in removing both As (III) and As (V). Several batch tests were conducted with different concentrations of arsenic at different pH conditions. During the batch tests, the maximum adsorption of As (III) occurred at a pH of 7.5, while As (V) adsorption reached its maximum value at a pH of 3. Both Langmuir and Freundlich adsorption models were found to fit with R-2 values greater than 0.92. From the Langmuir adsorption model, the maximum adsorption capacity of NZIS for As (III) and As (V) were estimated to be 1,250 and 500 mu g/g, respectively. These values were substantial enough to consider NZIS a promising new adsorbent for arsenic 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.

Many countries have waters contaminated with both herbicides and nitrates; however, information is limited with respect to removal rates for combined nitrate and herbicide elimination. This research investigates the removal of 2,4-D via denitrification, with a particular emphasis on the effect of adding naturally generated volatile fatty acids (VFAs). The acids were produced from an acid-phase anaerobic digester with a mean VFA concentration of 3153±801 mg/L (as acetic acid). Initially, 2,4-D degrading bacteria were developed in an SBR fed with both sewage and 2,4-D (30–100 mg/L). Subsequent denitrification batch tests demonstrated that the specific denitrification rate increased from 0.0119±0.0039 using 2,4-D alone to 0.0192±0.0079 g NO3-N/g VSS per day, when 2,4-D was combined with natural VFAs from the digester. Similarly, the specific 2,4-D consumption rate increased from 0.0016±0.0009 using 2,4-D alone to 0.0055±0.0021 g 2,4-D/g VSS per day, when using 2,4-D plus natural VFAs. Finally, a parallel increase in the percent 2,4-D removal was observed, rising from 28.33±11.88 using 2,4-D alone to 54.17±21.89 using 2,4-D plus natural VFAs.

This paper describes how the degradation of the organic fraction of municipal solid waste (OFMSW) is affected through co-digestion 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).