Comparison of maturation ponds and constructed wetlands as the final stage of an advanced pond system.

The treatment performance of a maturation pond (MP), the typical final polishing stage of an Advanced Pond System (APS), is compared with that of a surface-flow constructed wetland (CW) over 19 months. Both received approximately 67 mm d-1 of wastewater after passage through upstream stages of the APS. The MP, with greater sunlight exposure, had higher algal biomass (and associated suspended solids) than the CW, showed higher dissolved oxygen (DO) concentrations and greater diurnal variation in DO and pH. Neither polishing stages reduced nutrients markedly, with the CW exporting slightly more NH(3)-N and DRP, and less NO(3)-N than the MP. Disinfection was more efficient in the MP (geometric mean 1 log load removal, 12 MPN (100ml)-1) compared to the CW (0.47 log load removal, 53 MPN (100ml)-1). Incorporation of a final rock filter (28% of area) reduced median solids levels to < 10 g m(-3) in both the MP and CW. A hybrid between MPs and CWs with alternating zones of open-water (for enhanced disinfection and zooplankton grazing of algal solids) and wetland vegetation (promoting sedimentation and denitrification, and providing refugia for zooplankton) may provide more consistent effluent quality that either stage alone.

Constructed wetland attenuation of nitrogen exported in subsurface drainage from irrigated and rain-fed dairy pastures.

Nitrogen removal performance is reported for constructed wetlands treating subsurface drainage from irrigated and rain-fed dairy pastures in North Island, New Zealand. Flow-proportional sampling of inflow and outflow concentrations were combined with continuous flow records to calculate mass balances for the wetlands. Drainage flows from the irrigated catchment were 2.5-4 fold higher and N exports up to 5 fold higher per unit area than for the rain-fed catchment. Hydraulic and associated N loadings to the wetlands were highly pulsed, associated with rainfall, soil water status, and irrigation events. Transient pulses of organic nitrogen were an important form of N loss from the rain-fed landscape in the first year, and were very effectively removed in the wetland (> 90%). Median nitrate concentrations of approximately 10 g m(-3) in the drainage inflows were reduced by 15-67% during passage through the wetlands and annual nitrate-N loads by 16-61% (38-31 7 g N m(-2)y(-1)). Generation in the wetlands of net ammoniacal-N and organic-N (irrigated site) partially negated reduction in nitrate-N loads. The results show that constructed wetlands comprising 1-2% of catchment area can provide moderate reductions in TN export via pastoral drainage, but performance is markedly influenced by variations in seasonal loading and establishment/maturation factors.

Influence of biofilm on removal of surrogate faecal microbes in a constructed wetland and maturation pond.

The effect of biofilm on the attenuation of pathogen-sized particles from wastewater was compared for biofilms cultivated in a surface flow constructed wetland (SFW) and maturation pond (MP) The fate of fluorescently labelled microspheres (FLM) as surrogates for viruses (0.1 microm), bacteria (1 microm) and parasitic protozoa (4.5 microm dia) was investigated in microcosms in the presence or absence of biofilms. Rates of FLM removal from suspension were higher in the presence of biofilms for all particle sizes (kd 0.02-0.11 h(-1)) in MP and SFW microcosms with removal efficiency related to particle size and biofilm thickness and structure. Greater removal of 0.1 microm (79-81%), 1 microm FLM (92-96%) and 4.5 microm FLM (up to 98%) from suspension were found for microcosms containing thicker (autotrophic) biofilms grown in the MP or open water zone of the SFW. Lower removal of 43% (0.1 microm), 59% (1 microm) and 84% (4.5 microm) occurred in microcosms containing thinner heterotrophic biofilms from SFW vegetated zones. Providing surfaces for attachment of photosynthetic biofilms offers potential to enhance pathogen removal in open water systems. In vegetated systems, linkage to more oxic openwater zones may allow thicker and 'stickier' epiphytic biofilms to develop, improving pathogen interception and removal.

Oxygen flux implications of observed nitrogen removal rates in subsurface-flow treatment wetlands.

Nitrification, an oxygen-requiring microbial process, is generally considered the rate-limiting step for N removal in subsurface-flow constructed wetlands treating organic wastewaters. We used a simplified model of sequential N transformations and sinks to infer required rates of oxygen supply at 5 stages along experimental wetland mesocosms supplied with four different organic wastewaters with contrasting ratios of COD: N and forms of N. Mass balances of water-borne organic, ammoniacal and nitrate N, and plant and sediment N uptake showed average net rates of N mineralisation ranging from 0.22-0.53 g m(-2) d(-1), nitrification 0.56-2.15 g m(-2) d(-1), denitrification 0.47-1.99 g m(-2) d(-1) (60-84% of measured N removal) and plant assimilation 0.28-0.47 g m(-2) d(-1). The nitrogenous oxygen demand (NOD) required to support the observed nitrification rates alone was high compared to expected fluxes from surficial and plant-mediated oxygen transfer. In the presence of high levels of degradable organic matter (COD removal rates up to 66 g m(-2) d(-1)), heterotrophs with significantly higher oxygen affinities and energy yields are expected to outcompete nitrifiers for available oxygen. Problems with commonly held assumptions on the nature of coupled nitrification-denitrification in treatment wetlands are discussed.

Using constructed wetlands to treat subsurface drainage from intensively grazed dairy pastures in New Zealand.

Performance data, during the start-up period, are presented for constructed wetlands treating subsurface drainage from dairy pastures in Waikato (rain-fed) and Northland (irrigated), North Island, New Zealand. The wetlands comprised an estimated 1 and 2% of the drained catchment areas, respectively. Nitrate concentrations were high in the drainage inflows at both sites (medians 10 g m(-3) at Waikato and 6.5 g m(-3) at Northland), but organic N was also an important form of N at Waikato (37% of TN). Comparison of wetland inflow and outflow nutrient concentrations showed overall nutrient reductions during passage through the wetlands for NO3-N (34 and 94% for medians, respectively), TN (56 and 33%, respectively), and DRP (80%, Northland only). Median NH4-N (both sites) and DRP (Waikato) concentrations showed apparent increases between the wetland inlets and outlets. However, a mass balance calculated for the 3 month preliminary monitoring periods showed substantial mass removal of DRP (80%) and all measured forms of N (NO3-N 78%, NH4-N 41%, Org-N 99.8% and TN 96%) in the Waikato wetland. Monitoring of these systems needs to be continued through a range of seasons and years to fully assess their long-term performance.

Combined photosynthesis and mechanical aeration for nitrification in dairy waste stabilisation ponds.

New Zealand has 16,500 dairy farms (avg. 220 cows), with cows kept on pasture throughout the year. During the 9-month dairy season, the cows are milked twice a day (averaging 2.5-3 h per day in the dairy parlour). Urine and faecal wastes deposited in the dairy parlour are washed away with high pressure hoses, using large volumes of water. A common method of treatment is in simple two-pond (anaerobic/facultative) lagoon systems, which remove about 95% of suspended solids and BOD5, but only 75% of total-N prior to discharge. High concentrations of ammoniacal-N in the effluent can cause toxicity to aquatic organisms in receiving waters. Mechanical aeration of the second (facultative) lagoon to promote nitrification improves effluent quality by reducing oxygen demand and potential ammonia toxicity to streamlife. Mechanical aeration however is associated with considerable mixing, which may prevent algae from optimising photosynthesis in the facultative lagoon. A series of experiments was undertaken which tested the efficiency of mechanical aeration and then attempted to combine it with daytime algal oxygen production in order to maximise ammonia conversion to nitrate, while minimising costs to the farmer. An experimental facility was developed by dividing a large facultative lagoon into two, producing a matched pair of lagoons, operated in parallel with influent flow split equally. Over successive dairy seasons, various aeration regimes were compared. Continuous aeration promoted nearly complete nitrification of the ammoniacal-N (99% removal), and effluent BOD was approximately halved. However the continuous mixing reduced algal biomass, and thus daytime algal photosynthesis. Night-only aeration permitted greater algal photosynthesis to occur, as well as halving electrical power consumption. Ammoniacal-N removal reduced to 90% (10 g m(-3) remaining in the effluent), while BOD removal was also lower than in the continuously aerated lagoon (59 and 69% respectively). Providing a series of biofilm attachment surfaces for nitrifying bacteria by suspending geotextile material close to the surface in the pond in consistently aerobic water resulted in improved ammoniacal-N removal efficiency (93%) with night aeration, but still lower removal than continuous aeration.

Advanced pond system: performance with high rate ponds of different depths and areas.

Many domestic Wastewater Stabilisation Ponds (WSPs) or oxidation ponds in New Zealand require upgrading to reduce pollution of receiving waters. Advanced Pond Systems (APS) consisting of an Advanced Facultative Pond, High Rate Pond, Algae Settling Pond and Maturation Pond may provide a cost effective upgrade option. This paper presents the results of a 2-year study of the performance of two pilot APS systems with High Rate Ponds of different depths and areas. The HRPs of the APS systems both had the same flow rate (5 m3 d(-1)), volume (37.5 m3) and thus hydraulic retention time (7.5 d). However, the East HRP had an operating depth of 0.30 m and a surface area of 128 m2, and the West HRP had an operating depth of 0.45 m and a surface area of 85 m2. APS system performance was compared in terms of improvement of water quality. For nearly all parameters measured, there was little difference in performance between the two systems suggesting that the system with the smaller area could be used without affecting treatment. Comparison of final effluent with typical effluent of New Zealand WSPs showed that APS effluent was of higher quality and much less variable over time.

Dairy farm wastewater treatment by an advanced pond system.

Waste stabilisation ponds (WSPs) have been used for the treatment of dairy farm wastewater in New Zealand since the 1970s. The conventional two pond WSP systems provide efficient removal of wastewater BOD5 and total suspended solids, but effluent concentrations of other pollutants including nutrients and faecal bacteria are now considered unsuitable for discharge to waterways. Advanced Pond Systems (APS) provide a potential solution. A pilot dairy farm APS consisting of an Anaerobic pond (the first pond of the conventional WSP system) followed by three ponds: a High Rate Pond (HRP), an Algae Settling Pond (ASP) and a Maturation Pond (which all replace the conventional WSP system facultative pond) was evaluated over a two year period. Performance was compared to that of the existing conventional dairy farm WSP system. APS system effluent quality was considerably higher than that of the conventional WSP system with respective median effluent concentrations of BOD5: 34 and 108 g m(-3), TSS: 64 and 220 g m(-3), NH4-N: 8 and 29 g m(-3), DRP: 13 and 17 g m(-3), and E. coli: 146 and 16195 MPN/100 ml. APS systems show great promise for upgrading conventional dairy farm WSPs in New Zealand.

Linking pond and wetland treatment: performance of domestic and farm systems in New Zealand.

Wetland systems have been used extensively to supplement and upgrade waste stabilisation pond treatment systems in New Zealand. Key attributes of wetlands, such as low operational costs, minimal reliance on machinery and external energy inputs, high wildlife habitat values, and perceived "naturalness", complement those of pond systems. Performance data for a range of New Zealand post-pond constructed wetlands treating sewage, dairy farm and piggery wastewaters show BOD and SS concentrations can be readily reduced to low levels. Bacterial indicators are commonly reduced by at least one log unit, but levels below 500 cfu (100 mls)(-1) are difficult to achieve consistently. Nutrient removal efficiency is highly dependent on loading rates and wastewater characteristics. Plant establishment and maintenance, wildlife management, hydraulic design and adequacy of preceding treatment are identified as key practical issues in the implementation and management of constructed wetland systems.

Plants as ecosystem engineers in subsurface-flow treatment wetlands.

Mass balance performance data from side by side studies of planted and unplanted gravel-bed treatment wetlands with horizontal subsurface-flow are compared. Planted systems showed enhanced nitrogen and initial phosphorus removal, but only small improvements in disinfection, BOD, COD and suspended solids removal. Direct nutrient uptake by plants was insufficient to account for more than a fraction of the improved removal shown by planted systems. Roles of plants as ecosystem engineers are summarised, with organic matter production and root-zone oxygen release identified as key factors influencing nutrient transformation and sequestration.

Oligopeptide inhibitors of HIV-induced syncytium formation.

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein is essential for virus entry and the formation of multinucleated giant cells by cell fusion, one of the major virus-induced cytopathic effects. To study the effects of potential fusion inhibitors, a vaccinia virus recombinant expressing the envelope glycoprotein was generated and used to infect HeLa CD4+ cells. Syncytium induction was observed as early as 4 h postinfection and continued until the entire monolayer was fused. The N-terminus of the gp41 subunit of the HIV envelope protein is very hydrophobic, and appears to be involved in virus-induced membrane fusion. We synthesized several oligopeptide analogs of the N-terminal region of gp41 and determined their ability to inhibit HIV-induced cell fusion in CD4+ HeLa cells. A hexapeptide which was identical in amino acid sequence to the N-terminus of gp41 was found to completely inhibit cell fusion, whereas peptides with altered sequences showed reduced inhibitory activity. These peptides had no effect on protein synthesis, processing, or transport to the cell surface, and showed no signs of toxicity to cells even at very high concentrations. These results indicate that oligopeptides which are homologous to the fusion peptide of HIV inhibit virus-induced cytopathology, and should be evaluated further as potential antiviral agents.