Performance study of vegetated sequencing batch coal slag bed treating domestic wastewater in suburban area.

A practical and affordable wastewater treatment system serving small community in suburban areas was studied. The system was a vegetated sequencing batch coal slag bed integrated with the rhythmical movement of wastewater and air like that of a sequencing batch reactor. The removal mechanisms capitalized on the pollutant removal process in conventional constructed wetland. Cyperus alternifolius was planted into the coal slag bed to form a novel plant-soil-microbial interactive system. Nutrients in the domestic wastewater, which cause environmental nuisance like eutrophication, were targeted to be eliminated by the process design. Operated with the contact time of 18 h, the treatment systems achieved around 60% removal efficiency for carbonaceous matters. The removals of ammonia nitrogen and phosphorus were about 50% and 40%, respectively, while the removal of total suspended solids was approaching 80%. From the current study, the construction cost of the vegetated sequencing batch coal slag bed was 256 RMB/m3 and the operation cost was 0.13 RMB/m3. With the advantages of ease of operation, low costs, desirable treatment efficiency and aesthetic value, the vegetated sequencing batch coal slag bed is proposed to be an alternative for onsite domestic wastewater treatment in suburban areas.

Treatment of odorous volatile fatty acids using a biotrickling filter.

In this study, a novel fibrous bioreactor was developed for treating odorous compounds present in contaminated air. The first stage of this work was a preliminary study which aimed at investigating the feasibility of using the fibrous bioreactor for the removal of malodorous volatile fatty acids (VFA) that is a common odorous contaminant generated from anaerobic degradation of organic compounds. The kinetics of microbial growth and VFA degradation in the selected culture, and the performance of the submerged bioreactor at different VFA mass loadings were studied. Above 95% of VFA removal efficiencies were achieved at mass loadings up to 22.4 g/m(3)/h. In the second stage, the odour treatment process was scaled up with system design and operational considerations. A trickling biofilter with synthetic fibrous packing medium was employed. The effects of inlet VFA concentration and empty bed retention time (EBRT) on the process performance were investigated. The bioreactor was effective in removing VFA at mass loadings up to 32 g/m(3)/h, beyond which VFA started to accumulate in the recirculation liquid, indicating the biofilm was unable to degrade all of the VFA introduced. Although VFA accumulated in the liquid phase, the removal efficiency remained above 99%. This suggested that the biochemical reaction rather than gas-liquid mass transfer was the limiting step of the treatment process. In addition, the biotrickling filter was stable for long-term operation with relatively low and steady pressure drop, no clogging and degeneration of the packing material occurred during the four-month study.

Nocardia foaming control in activated sludge process treating domestic wastewater.

In this study, filamentous bacteria (Nocardia amarae) were identified as the major causal microorganism in foaming sludge. The results of growth kinetics study indicated that N. amarae had a relatively strong affinity for non-readily biodegradable fatty acids. N. amarae was able to consume various fatty acids at a constant growth yield from 0.413 to 0.487 g/gCOD. Under common F/M ratio (less than 0.5 g BOD/gMLSS/d) used in activated sludge processes, specific growth rate of N. amarae was found to be more significant than that of non-filamentous bacteria. Based on this feature, a novel technique feast-fast operation (FFO) was developed for the foaming control. The sludge volume index (SVI) rapidly decreased from 300 to 80 mL/g and further stabilized at about 70 mL/g and the system was free from stable foam, while the BOD removal efficiency was maintained above 95%. This control technology effectively suppressed the overgrowth of filaments and improved the settleability of activated sludge without adverse effects on the treatment performance and the process stability.

Synthesis of PHAs from waster under various C:N ratios.

Polyhydroxyalkanoates (PHAs) production was carried out under various C:N ratios. A ratio of 100 resulted best polymer yield. C-source was an important factor in synthesis. For example, as the ratio of valeric acid (C5) to butyric acid (C4) in N-free medium was increased, the mole fraction of HV in the copolymer increased. When soy waste was used as a C-source a copolymer, a high HV mole fraction (HB:HV, 75:25) was produced while when malt waste was used, a much lower HV mole fraction (HB:HV, 90:10) was generated. It was concluded that activated sludge bacteria could be induced to produce PHAs using food wastes as C-sources and this could be the basis for production of biodegradable plastics.

Synthesis of polyhydroxyalkanoate (PHA) from excess activated sludge under various oxidation-reduction potentials (ORP) by using acetate and propionate as carbon sources.

Accumulation of poly hydroxyalkanoate (PHA) from excess activated sludge (EAS) was monitored and controlled via the oxidation-reduction potential (ORP) adjusting process. The ORP was adjusted and controlled by only regulating the gas-flow rate pumped into the cultural broth in which sodium acetate (C2) and propionate (C3) were used as carbon sources. Productivity of PHA and the PHA compositions at various C2 to C3 ratios were also investigated. When ORP was maintained at +30 mV, 35% (w/w) of PHA of cell dry weight obtained when C2 was used as sole carbon source. The PHA copolymer, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), accumulated by EAS with different 3-hydroxyvalarate (3HV) molar fractions ranged from 8% to 78.0% when C2 and C3 was used as sole carbon source, By using ORP to monitor and control the fermentation process instead DO meter, the ORP system provided more precise control to the PHA accumulation process from EAS under low dissolved oxygen (DO) concentrations. Adjusting the C2 to C3 ratios in the media could control the composition such as the 3HV/3HB ratios of the PHBV. Furthermore, it might be an effective way to adjust the 3HV molar fractions in PHBV by controlling the DO concentration via the ORP monitoring system. The 3HV molar fractions in the PHBV declined with increasing ORP from -30 mV to +100 mV by adjusting the gas-flow rate (i.e. the DO concentration). It is concluded that the DO plays a very important role in the synthesis of 3HV subunits in PHBV co-polymer from the EAS. Therefore, a hypothetic metabolic model for PHA synthesis from EAS was proposed to try to explain the results in this study.

A combined bioprocess for integrated removal of copper and organic pollutant from copper-containing municipal wastewater.

Heavy metal-containing wastewater is difficult to treat by most of the bioprocess due to its toxicity to microorganism in activated sludge. In this study, a combined bioprocess consisting of biosorption section that contained magnetite immobilized Pseudomonas putida 5-x cell as biosorbent followed by sequence batch reactor (SBR) was developed to treat Cu(2+)-containing municipal wastewater. The production techniques of Pseudomonas putida 5-x cell as biosorbent, such as optimal cell harvest period and cell pretreatment techniques were studied. Experimental results showed, considering both cell biomass and cell adsorption capacity to Cu(2+), 36 h is the optimal harvest period in the course of culturing Pseudomonas putida 5-x cells as biosorbent, and 0.1-0.3 mol L(-1) HCl is an optimal cell pretreating eluant to improve Cu(2+) adsorption capacity. The performances of the combined bioprocess for treating Cu(2+) containing wastewater were assessed. Experimental results showed that after treatment by biosorption, the Cu(2+) level in wastewater was reduced to level that did not inhibit COD removal efficiency of subsequent SBR activated sludge process, although it still affected the COD adsorption capacity of activated sludge. In terms of COD removal, the biosorption section was efficient for reducing Cu(2+) concentration to provide biodegradable wastewater for subsequent SBR activated sludge process.

Role of cell surface components on Cu2+ adsorption by Pseudomonas putida 5-x isolated from electroplating effluent.

A gram-negative bacterium Pseudomonas putida 5-x with high Cu2+ accumulating capability was isolated from electroplating effluent in Kwun Tong, Hong Kong. The pretreated cells without superficial layer-capsule, isolated cell envelopes and the separated peptidoglycan layer materials were obtained from fresh P. putida 5-x cells, their Cu2+ adsorption capacities and properties were compared with that of the fresh cells. Pretreatment by 0.1 mol L(-1) HCl enhanced Cu2+ adsorption capacity due to the degradation of cell superficial layer-capsule of P. putida 5-x cells. Isolated cell envelopes possessed five times more Cu2+ adsorption capacity than that of fresh intact cell. The Cu2+ adsorption of separated peptidoglycan layer materials indicated that the peptidoglycan layer only played 10-15% part of the Cu2+ adsorption capacity, and implied other cell surface components such as outer membrane or inner membrane might play an important role in such high Cu2+ binding of the cell envelopes. The adsorption process of fresh cells, pretreated cells and cell envelopes of P. putida 5-x could be described with Freundlich isotherm, while the adsorption of Cu2+ by separated peptidoglycan layer materials was better described with Langmuir isotherm.

Assessment of heavy metal cations in sediments of Shing Mun River, Hong Kong.

The extent of heavy metal cation contamination in the Shing Mun River has been assessed. Sediment samples were taken at eight strategic locations along the river system. The highest concentrations of copper (Cu, 1.66 mg/g), lead (Pb, 0.354 mg/g), zinc (Zn, 2.2 mg/g) and chromium (Cr, 0.047 mg/g) were found in the Fo Tan Nullah, a major tributary of the Shing Mun River. The highest concentrations of aluminum (114 mg/g) and cadmium (Cd, 0.047 mg/g) were found in the Shing Mun Main River Channel. These contaminated sediments, accumulated over the years on the river bed, could act as secondary sources of pollution to the overlying water column in the river.

Nutrient release and sediment oxygen demand in a eutrophic land-locked embayment in Hong Kong.

Tolo Harbour is a large eutrophic land-locked estuarine embayment in Hong Kong. The rapid urbanization, commercio-industrial activities and lack of legislative control around the Tolo catchment produced large quantities of untreated or partially treated municipal sewage, agricultural wastes and cottage industrial effluents which were discharged into Tolo Harbour via rivers and watercourses. Control measures were implemented to reduce the external nutrient loading into the harbour since the early 1980s. Nutrient data for the period 1982 to 1997 were analyzed for temporal trends. Over the period of observation, the total inorganic nitrogen and total phosphorus both show an increasing trend, despite a decade of efforts in reducing nutrient loading. The release rates of potentially mobile nitrogen (N) and phosphorus (P) from the sediments collected from Tolo Harbour were determined by N and P release experiments under oxic conditions. The experimental results showed that the sediment released significant amount of nutrients, especially orthophosphates and ammonia nitrogen. The maximum release rates were 15.0 and 206.0 mg/m2/day, respectively. Although the external nutrient loading has been reduced, nutrients could gradually be released back into the water column from the contaminated sediments and delay improvement of the water quality.

The degradation of xenobiotic branched carboxylic acids in anaerobic sediment of the Pearl River in Southern China.

Xenobiotic branched carboxylic acids (BCAs) discharged by industries are often persistent in biological wastewater treatment systems and end up in water and sediments. In this study, the degradation of 12 typical BCAs in an anaerobic environment of river sediment was studied in vitro using enrichment shake-flask cultures. The anaerobic consortium taken from the river sediment, comprising BCA-degrading and methane-producing genera, degraded BCAs with tertiary carbons through beta-oxidation, followed by methanogenesis mechanisms. The maximum cell densities in the cultures using BCAs as the sole carbon source ranged between 5.0 and 6.0 x 10(5) cells/ml. The maximum degradation rates were between 5.0 and 8.5 x 10(-3) mmol/h. The consortium could not degrade BCAs with quaternary carbons. The degree of branching at the alpha or beta position along the carbon chain interfered with the beta-oxidation mechanisms. These BCAs would accumulate in the sediment and significantly affect the cycling of organic carbon and nutrients.

Effects of trace levels of copper, chromium, and zinc ions on the performance of activated sludge.

The effects of copper, chromium, and zinc ions, at trace levels, on the performance of a simulated activated sludge process were investigated. The results of batch adsorption experiments showed that the adsorption of copper, chromium, and zinc ions followed both the Langmuir and Freundlich isotherms. The presence of trace levels of these three metals not only reduced the adsorption rate of organic matters but also the chemical oxygen demand adsorption capacity (CAC) of the activated sludge. Metal ions competed with the organic substrate for adsorption binding sites on the surfaces of activated sludge bioflocs and reduced the CAC. Studies performed in a sequential batch reactor (SBR) showed that the presence of trace levels of heavy metal ions in wastewater affected the SBR performance to different extents depending on the hydraulic retention time (HRT). When the reactors were operated at short HRTs of 2.5 d or less, the presence of trace levels of heavy metal ions reduced substantially the CAC of activated sludge, which, in turn, affected significantly the performance of the SBR. However, under longer HRTs (e.g., 5 d), the heavy metal ions in the wastewater reduced the CAC but had no significant effect on the chemical oxygen demand removal efficiency.

Effect of food:microorganism ratio in activated sludge foam control.

Foaming is a common operational problem in activated sludge processes that often adversely affects the quality of the treated effluent. Overgrowth of the filamentous Nocardia spp. in the microbial ecosystem was previously identified as the cause of foaming. In the present study, the specific growth rate of Nocardia amarae was found to be much higher than that of nonfilamentous bacteria under food:microorganism (F:M) ratios lower than 0.5 mg of biological oxygen demand (BOD)/(mg of mixed liquor suspended solids [MLSS].d). This indicated that filamentous overgrowth may occur in normal activated sludge processes that are continually operated under the usual F:M range of 0.2-0.6 mg of BOD/(mg of MLSS.d). A novel two-component feast-fast operation (FFO) that capitalized on the sensitivity of filamentous bacteria to F:M ratio was designed to prevent and control foaming problems. The F:M ratio in the "feasting" aeration unit was 0.8 mg of BOD/(mg of MLSS.d) whereas that in the "fasting" aeration unit was 0.2 mg of BOD/(mg of MLSS.d). The FFO resulted in an overall process F:M ratio that still remained within the normal range, while avoiding prolonged exposure of the activated sludge ecosystem to an F:M ratio below 0.5 mg of BOD/(mg of MLSS.d). The FFO suppressed the overgrowth of filamentous bacteria without adversely affecting the organic treatment efficiency of the modified process.

Degradation pathway of persistent branched fatty acids in natural anaerobic ecosystem.

Branched fatty acids (BAFs) in industrial effluents are often persistent in biological wastewater treatment systems and end up as organic contaminants in the water environment. In this study, degradation of eight characteristic BAFs in a natural anaerobic ecosystem of an eutrophic river sediment was studied in vitro by enrichment culture techniques. The anaerobic consortium, comprising of BFA-degrading and methane-producing genera, degraded BFAs with a tertiary carbon through beta-oxidation followed by methanogenesis mechanisms. The consortium could not degrade BFAs with a quaternary carbon. The degree of branching at the alpha or beta position along the carbon chain interfered with the beta-oxidation mechanisms, and hence affected the degradability of the compound.

Sub-lethal effects of heavy metals on activated sludge microorganisms.

The effects of heavy metals, at sub-lethal concentrations, on activated sludge microbial ecosystem were investigated. Adsorption capacity and rate of copper, chromium, lead and zinc on microbial flocs were much faster than that of organic matters. Metals affected not only the adsorption rate of organic matters but also the COD adsorption capacity of the activated sludge. Effects of heavy metals, on wastewater treatment performance of a sequencing batch reactor were also studied. Metal-laden wastewater at sub-lethal levels affected the performance to different extents, depending on the hydraulic retention time. Metal ions acted as a strong competitor against the organic compounds for active sites on the bioflocs instead of acting as a toxic microbial inhibitor, thus hampering organic adsorption and affecting the COD removal efficiency under shorter HRTs.