Land Area Requirement Research Articles

Land substitution effects of biofuel side products and implications on the land area requirement for EU 2020 biofuel targets

The provision of biofuels today is based on energy crops rather than residual biomass, which results in the requirement of agricultural land area. The side products may serve as animal feed and thus prevent cultivation of other feedstock and the use of corresponding land area. These effects of biofuel provision have to be taken into account for a comprising assessment of land area requirement for biofuel provision. Between 18.5 and 21.1 Mio. hectares (ha) of land area is needed to meet the EU 2020 biofuel target depending on the biofuel portfolio when substitution effects are neglected. The utilization of the bioethanol side products distiller′s dried grain and solubles (DDGS) and pressed beet slices may save up to 0.7 Mio. ha of maize cultivation area in the EU. The substitution effect due to the utilization of biodiesel side products (oil cakes of rape, palm and soy) as animal feed may account for up to 7.1 Mio. ha of soy cultivation area in Brazil. The results show that the substitution of land area due to use of side products might ease the pressures on land area requirement considerably and should therefore not be neglected in assessing the impacts of biofuel provision worldwide.

Evaluation of biological pond system modified with submerged planted dams

Pond systems have been studied in Uzbekistan for about 30 years and are widely perceived as an effective and cost-efficient solution to many of the issues that arise with conventional wastewater treatment options. This paper reviews and analyzes observations and data collected since 1995 when a full-scale biopond (BP) system was constructed for the purpose of purifying domestic wastewater from the village of Charvak Hydro Power Station. The Charvak BP system was designed with a single facultative pond (FP) that feeds into two consecutive vegetated pond (VP) cells. Each of these cells is then laterally divided into even increments by submerged planted dams, the surface area of which comprises 31% of the entire cell's surface. This system has proven itself proficient in the reduction of contaminants vis-à-vis natural processes, achieving an average elimination of 76% chemical oxygen demand (COD), 93% 5-day biological oxygen demand (BOD5), 80% total suspended solids (TSS), and 89% ammonia nitrogen (NH 4–N). Helminthes eggs removed via sedimentation were not detected in the final effluent. Additionally, seasonal characteristics are presented. The advantages of this system include a high efficiency in organic and NH 4–N removal with less prohibitive land area requirements relative to conventional wetland systems.

Identifying plant species with root associated bacteria that promote nitrification and denitrification in ecological treatment systems

Plant-based systems, such as wetlands and other ecological treatment systems, are promising, sustainable alternatives to conventional wastewater treatment. One of the biggest drawbacks of these systems when compared with conventional wastewater treatment systems is a large land area requirement; thus greater efficiency is needed to reduce land requirements and consequent costs. This research identified plant species that promote greater nitrogen removal, and whose use could lead to increased efficiency of ecological treatment systems. Potential nitrification and denitrification rates of bacteria associated with the roots of herbaceous species (Cyperus papyrus, Colocasia esculentus), and woody species (Hibiscus moscheutus and Salix nigra) were measured in the lab. Potential nitrification rates were determined from the rate of NO 3 − accumulation in microcosms containing wastewater and live plants. Potential denitrification was measured using the acetylene inhibition technique on microcosm incubations of filtered wastewater and plant roots. Significantly more NO 3 − (mg 1−1 hr−1) was produced by bacteria associated with S. nigra and C. papyrus roots than in microcosms containing only wastewater, or H. moscheutus, (P < 0.001). Potential denitrification rates were significantly greater in H. moscheutos and S. nigra root microcosms than in C. esculentus and C. papyrus root microcosms on dry weight, wet weight and root area bases (P < 0.001). These results demonstrate that the efficiency of ecological treatment systems treating wastewater high in NH 4 + would be improved with a mix of herbaceous and woody species, whereas wastewater high in NO 3 − would be most efficiently treated with woody species. Thus, a diversity of species is needed to optimize ecological treatment system function.

Nitrogen transformation in a denitrification layer irrigated with dairy factory effluent

Adoption of land-based effluent treatment systems can be constrained by the costs and availability of land. Sufficient land area is needed to ensure nitrate leaching from applied effluent is minimised. One approach to decrease required land area is to enhance N removal by denitrification. Layers of organic matter (100mm thick) were installed below topsoil of a site irrigated with dairy factory effluent. These “denitrification” layers were tested to determine whether they could decrease nitrate leaching by increasing denitrification. Four plots (10×10m2 each) were constructed with a denitrification layer installed at 300mm below the surface, and N losses were measured in leachate using suction cups every 3 weeks for 19 months. N in leachate was compared with 4 control plots. Denitrifying enzyme activity, nitrate concentrations, and carbon availability were measured in samples collected from the denitrification layers. These measurements demonstrated that denitrification occurred in the layer; however, denitrification rates were not sufficiently high to significantly decrease nitrate leaching. Total N leaching was 296kgNha−1 from control plots and 238kgNha−1 from plots with denitrification layers; a total of 798kgNha−1 was applied in effluent. More than 50% of the leached N to 40cm was as organic N, presumably due to bypass flow. Other studies have demonstrated that thicker denitrification layers (more than 300mm) can reduce nitrate leaching from small-scale septic tank drainage fields but this study suggests that it is probably not practical to use denitrification layers at larger scales.

Rotating biological contactors: a review on main factors affecting performance

Rotating biological contactors (RBCs) constitute a very unique and superior alternative for biodegradable matter and nitrogen removal on account of their feasibility, simplicity of design and operation, short start-up, low land area requirement, low energy consumption, low operating and maintenance cost and treatment efficiency. The present review of RBCs focus on parameters that affect performance like rotational speed, organic and hydraulic loading rates, retention time, biofilm support media, staging, temperature, influent wastewater characteristics, biofilm characteristics, dissolved oxygen levels, effluent and solids recirculation, step-feeding and medium submergence. Some RBCs scale-up and design considerations, operational problems and comparison with other wastewater treatment systems are also reported.

Optimal choice of wastewater treatment train by multi-objective optimization

The typical domestic wastewater treatment train consists of some combination of unit operations for preliminary, primary, secondary, tertiary, and advanced treatment, and residual management, with many options being available for each type of unit operation. The challenge is to select treatment trains for which the extent and reliability of treatment are high, whereas the capital, operation and maintenance (O&M) costs of the treatment and land area requirement are low. This proposition has been formulated as a multi-objective optimization problem, and solved using the evolutionary/genetic optimization technique. The inputs required are the capital costs, O&M costs, land area requirements, and reliabilities of the unit operations of various types. In addition, overall environmental cost (E) corresponding to various treatment trains is input as a normalized parameter, which can take values in the range 0–100, with E being 100 corresponding to the ‘no treatment’ option. In other cases, E is a function of both treatment train efficiency and reliability. The problem was solved to determine the Pareto optimal, i.e. ‘no worse’ than each other, set of solutions under three conditions, viz. when E was not constrained, and for E<75, and E<50. Correctness of the algorithm was probed through a threefold analysis, (1) by solving a simplified two-objective problem, (2) by demonstrating the efficiency of the algorithm in picking up ‘sure-optimal’ solutions, i.e. solutions deliberately made optimal through manipulation of input data, and (3) by demonstrating that the set of optimal solutions remains approximately the same irrespective of the variations in the initial population size chosen for the genetic operations.

Powering the planet: Chemical challenges in solar energy utilization

Global energy consumption is projected to increase, even in the face of substantial declines in energy intensity, at least 2-fold by midcentury relative to the present because of population and economic growth. This demand could be met, in principle, from fossil energy resources, particularly coal. However, the cumulative nature of CO(2) emissions in the atmosphere demands that holding atmospheric CO(2) levels to even twice their preanthropogenic values by midcentury will require invention, development, and deployment of schemes for carbon-neutral energy production on a scale commensurate with, or larger than, the entire present-day energy supply from all sources combined. Among renewable energy resources, solar energy is by far the largest exploitable resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans in an entire year. In view of the intermittency of insolation, if solar energy is to be a major primary energy source, it must be stored and dispatched on demand to the end user. An especially attractive approach is to store solar-converted energy in the form of chemical bonds, i.e., in a photosynthetic process at a year-round average efficiency significantly higher than current plants or algae, to reduce land-area requirements. Scientific challenges involved with this process include schemes to capture and convert solar energy and then store the energy in the form of chemical bonds, producing oxygen from water and a reduced fuel such as hydrogen, methane, methanol, or other hydrocarbon species.

Constructed Wetlands and Waste Stabilization Ponds for Small Rural Communities in the United Kingdom: A Comparison of Land Area Requirements, Performance and Costs

Land area requirements for secondary subsurface horizontal-flow constructed wetlands (CW) and primary and secondary facultative ponds with either unaerated or aerated rock filters were determined for three levels of effluent quality: that specified in the Urban Waste Water Treatment Directive (UWWTD) (≤25 mg filtered BOD l−1 and ≤150 mg SS l−1 for waste stabilization ponds (WSP) effluents, and ≤25 mg unfiltered BOD l−1 for CW effluents (mean values); and two common requirements of the Environment Agency: ≤40 mg BOD l−1 and ≤60 mg SS l−1, and ≤10 mg BOD l−1, ≤15 mg SS l−1 and ≤5 mg ammonia-N l−1 (95-percentile values). A secondary CW requires 60 percent more land than a secondary facultative pond to produce an UWWTD-quality effluent, 38 percent more land than a secondary facultative pond and an unaerated rock filter to produce a 40/60 effluent and, were it to be used to produce a 10/15/5 effluent, it would require ∼480 percent more land than a secondary facultative pond and an aerated rock filter. Its estimated 2005 cost is £1100-2600 p.e.−1, whereas that of a primary facultative pond and rock filter is ∼£400 p.e.−1. On the basis of land area requirements, performance and cost, facultative ponds and unaerated or aerated rock filters are to be preferred to secondary subsurface horizontal-flow constructed wetlands.

Use of mobile fast pyrolysis plants to densify biomass and reduce biomass handling costs—A preliminary assessment

ROI BioOil plants can be made modular and transportable, allowing them to be located close to the source of biomass and the subsequent transportation of high energy density BioOil to a central plant. Conversely, one central BioOil plant could supply several energy users in distributed locations, or several plants could supply numerous end-users, just as in the petroleum industry. Renewable Oil International® LLC (ROI) is one of several developers of fast pyrolysis technology. The production of BioOil can convert raw biomass into a low-viscosity liquid that, depending on the moisture content of the feedstock, increases the energy density of biomass by a factor of 6 to 7 times over green wood chips. The increase in energy density increases the amount of energy that can be hauled by standard tanker trucks versus a chip trailer van by a factor of two. Capital costs, exclusive of land costs, are comparable for a 50 MWe biomass handling system at the power plant. Land area requirements for fuel storage and handling are reduced roughly half for BioOil systems versus solid fuel handling systems. No analysis was made of operating and maintenance costs.

Effect of Control Plot Density, Control Plot Arrangement, and Assumption of Random or Fixed Effects on Nonreplicated Experiments for Germplasm Screening Using Spatial Models

Early generation selection experiments typically involve several hundred to thousands of lines. Various systematic and statistical techniques have been developed to increase effectiveness and efficiencies in such experiments, including the development and application of spatial statistical models. In this study, mixed model equations were used to provide least squares means (LSMEANs) and best linear unbiased predictors (BLUPs) and compare selection effectiveness and efficiencies to observed (Y) and true values in simulated experiments varying in size (10 × 10, 20 × 20 and 30 × 30 grids), control plots densities (0, 5, 10, 20, and 50%), control plot arrangements (high, medium, and low A‐optimality), and spatial range of influence (short and long). Results were similar for all grid sizes. In experiments in which the simulated land areas were highly variable (short range), none of the predictors, Y, LSMEAN, or BLUP, were very effective in identifying the true superior genotypes. When the simulated land areas were less variable (long range), use of BLUPs consistently resulted in the highest proportion of true top ranking genotypes identified across all control plot densities, while using the observed values consistently resulted in identification of the lowest proportion of the true top ranking genotypes. Effectiveness of LSMEANs was dependent on control plot density and arrangements. Use of BLUPs for early generation germplasm screening experiments should result in a high effectiveness in selecting truly superior germplasm and high efficiency because of the ability to account for spatial variability with the use of few or no control plots.

Anaerobic reactor/high rate pond combined technology for sewage treatment in the Mediterranean area

Two high-rate, anaerobic/aerobic units were used to treat the sewage of the Institut Agronomique st Vétérinaire Hassan II (Morocco) campus in a 1,100 m2-plant designed for 1,500 e.p. and receiving 63 m3 per day. The anaerobic pre-treatment consisted of a two-step up-flow anaerobic reactor (TSUAR) comprising two reactors and one external settler all in series. The aerobic line, or post-treatment, consisted of a high-rate algal pond (HRAP) and one maturation pond in series. The system totalized a hydraulic retention time (HRT) of 9 days. A gravel filter (GF) was constructed behind the TSUAR to trap low-density particles. The TSUAR removed 80% of COD and 90% of SS within 48 h. Solids retention time in the reactors averaged 32 d with a specific sludge production of 0.28 g SS g(-1) COD removed. Almost 93% of the sludge evacuated from the settler was stabilized. Specific biogas production from both reactors was 0.25m3 kg(-1) COD removed. Used in this configuration, the HRAP lost its BOD removal activity and increased its nutrients and pathogens removal capabilities (tertiary treatment). Results showed that 85% of total nitrogen and 48% of total phosphorus were removed by the HRAP. Land area requirement of this combination was less than 1 m2 per capita and filtered final effluent was of excellent quality (COD, 82 mg/l; TKN, 8.3 mg/l; total P, 2.7 mg/l, faecal coliforms, 2.4 10(3)/100 ml and zero helminths eggs).

OPTIMIZATION PROCEDURE FOR COST EFFECTIVE BMP PLACEMENT AT A WATERSHED SCALE1

ABSTRACT: A combinatorial optimization procedure for best management practice (BMP) placement at the watershed level facilitates selection of cost effective BMP scenarios to control non point source (NFS) pollution. A genetic algorithm (GA) was selected from among several optimization heuristics. The GA combines an optimization component written in the C++ language with spatially variable NFS pollution prediction and economic analysis components written within the Arc View geographic information system. The procedure is modular in design, allowing for component modifications while maintaining the basic conceptual framework. An objective function was developed to lexicographically optimize pollution reduction followed by cost increase. Scenario cost effectiveness is then calculated for scenario comparisons. The NPS pollutant fitness score allows for evaluation of multiple pollutants, based on prioritization of each pollutant. The economic component considers farm level public and private costs, cost distribution, and land area requirements. Development of a sediment transport function, used with the Universal Soil Loss Equation, allows the optimization procedure to run within a reasonable timeframe. The procedure identifies multiple near optimal solutions, providing an indication of which fields have a more critical impact on overall cost effectiveness and flexibility in the final solution selected for implementation. The procedure was demonstrated for a 1,014‐ha watershed in the Ridge and Valley physiographic region of Virginia.

The reasons behind the performance superiority of a high rate algal pond over three facultative ponds in series

Results from a tracer study were used to determine and to compare actual and standard (k(20 degrees C)) first order reaction rate constants for COD removal in a High Rate Algal Pond (HRAP) and in 3 facultative ponds (FP) in series. An annual average k(20 degreesC) of 0.123 day(-1) was found for the HRAP while the values of 0.097, 0.025 and 0.003 d(-1) were found for facultative ponds 1, 2 and 3 respectively. Also, comparing nominal and tracer study hydraulic retention times showed large differences for the FP but not for the HRAP indicating that the former were suffering from severe short-circuiting. Loading rate within the range of operation exhibited a positive correlation with k(20 degrees C) for the HRAP but did not show such a relationship for any of the FP. Optimal chlorophyll-a concentration was found to be 3 mg/l for the HRAP and only 1.1 mg/l for the FP. Pollutant specific removal rates (SRR), that translate the hydrodynamic efficiency and the rate of COD biodegradation into pond performance per m2 and per day were calculated. They show that the adoption of the HRAP in place of a series of 3 FP reduces the net land area requirement (LAR) by at least 40%.

Emission of H2S and mass balance of sulfur in anaerobic ponds

Anaerobic ponds are highly efficient at removing BOD from wastewater with a reduced land area requirement. However, their use is often limited because of the problem of odor release, primarily due to the emission of hydrogen sulfide (H2S). The experiments were conducted on full scale anaerobic ponds used for the primary treatment of urban wastewater under Mediterranean climatic conditions (south of France). A model was developed to estimate the emission of H2S from water characteristics (temperature, pH and sulfides concentration). The emission rate from anaerobic ponds varied between 20 and 576 mg-S/m2.d, leading to concentrations of H2S in the surrounding atmosphere between 0.2 and 5.2 ppm. These concentrations risked creating odor nuisances for nearby inhabitants. The whole of the results and the analysis of sulfur species in sludge permitted the production of a complete mass balance for sulfur. Methods of reducing the emission of odorous compounds were tested on a large scale. The recirculation of secondary effluent and the use of impermeable or permeable covers appeared to be the most interesting solutions.

Recovery of dairy manure nutrients by benthic freshwater algae

Harnessing solar energy to grow algal biomass on wastewater nutrients could provide a holistic solution to nutrient management problems on dairy farms. The production of algae from a portion of manure nutrients to replace high-protein feed supplements which are often imported (along with considerable nutrients) onto the farm could potentially link consumption and supply of on-farm nutrients. The objective of this research was to assess the ability of benthic freshwater algae to recover nutrients from dairy manure and to evaluate nutrient uptake rates and dry matter/crude protein yields in comparison to a conventional cropping system. Benthic algae growth chambers were operated in semi-batch mode by continuously recycling wastewater and adding manure inputs daily. Using total nitrogen (TN) loading rates of 0.64–1.03 g m −2 d −1 , the dried algal yields were 5.3–5.5 g m −2 d −1 . The dried algae contained 1.5–2.1% P and 4.9–7.1% N. At a TN loading rate of 1.03 g m −2 d −1 , algal biomass contained 7.1% N compared to only 4.9% N at a TN loading rate of 0.64 g m −2 d −1 . In the best case, algal biomass had a crude protein content of 44%, compared to a typical corn silage protein content of 7%. At a dry matter yield of 5.5 g m −2 d −1 , this is equivalent to an annual N uptake rate of 1430 kg ha −1 yr −1 . Compared to a conventional corn/rye rotation, such benthic algae production rates would require 26% of the land area requirements for equivalent N uptake rates and 23% of the land area requirements on a P uptake basis. Combining conventional cropping systems with an algal treatment system could facilitate more efficient crop production and farm nutrient management, allowing dairy operations to be environmentally sustainable on fewer acres.

Feasibility of waste stabilization pond technology for small municipalities in Colombia

The selection of any wastewater treatment technology should take into consideration both "software" and "hardware" aspects. There are contrasting opinions regarding the feasibility of waste stabilisation ponds (WSP): some emphasise their advantages while others are concerned with their high land area requirements. As with any technology, WSP are feasible under specific circumstances related to the context where they are to be implemented. In this study data were collected from three regions in Colombia (Nariño, Tolima and Valle del Cauca) in order to assess the feasibility of WSP under real conditions in a tropical country. A feasibility matrix was developed in order to organise and synthesise the information gathered. The results obtained showed that WSP are highly feasible in Tolima and Valle del Cauca due to the fact that these regions have geographical, socio-economic and technical characteristics that enhance the advantages of WSP technology. Nariño has a very mountainous topography along with other local limitations that hinder the application of WSP technology. The cost of land was not found to be a real limitation for the technology, whereas the availability of land is. Finally, the feasibility matrix may be a good planning tool at regional or national levels in order to help decision-making regarding cost-effective wastewater treatment alternatives on the basis of local conditions.

DETERMINING PHOSPHORUS IN BIOSOLIDS: USING A NEUTRAL AMMONIUM CITRATE EXTRACTION

More frequent occurrences of major fish kills and more focus on watershed management have recently increased efforts to better control non-point sources of pollution. Land applied materials, such as biosolids and manure, are major sources of agricultural nutrients. A major focus is being placed on phosphorus (P) management, since it is often applied in excess of crop requirements via organic P sources. Some states are implementing, or at least considering, Pbased land application rates, instead of the traditional nitrogen (N) based application rates. With N-based application rates, P is typically over-applied. If P-based (limiting) application rates are used, biosolid land application programs could be significantly restricted due to P limitations. Additionally, the N-needs of the crops would not be met. Farmers would be forced to apply supplemental N fertilizers to meet crop needs. The P Index tool is being developed by the Natural Resources Conservation Service. It is being considered by more than 20 states as a way of evaluating P risk. The purpose of the P Index is to provide a method of assessing various landforms and management practices for potential risk of P movement to water bodies. One component of the P Index is the organic P source application rate. Not all of the P contained in organic P sources (i.e., biosolids and manure) represents an immediate threat to the surrounding environment. Therefore, identifying a method of P determination (other than total P measurement) in organic P sources is becoming critical. An appropriate method of P determination in biosolids must be identified. Because of the varying characteristics of biosolids, a “one-size-fits-all” measure, such as total P, is not appropriate. Some measure of plant available (bioavailable) P is preferred. Overestimating plant available P with P-based application rates could result in increased land area requirements for biosolids disposal as well as supplemental N fertilizer requirements. Underestimating plant available P could compromise the surrounding water quality. Unfortunately, the P issue is more complicated than considering only one parameter. This illustrates the need for a tool such as the P Index. By improving the accuracy of each of the parameters, the P Index could become a very powerful tool for biosolids managers. This paper presents the results of recently completed work and the implications of its findings. Thirty-seven biosolids, representing a range of treatment processes were analyzed for extractable P using the neutral ammonium citrate (NAC) procedure. Various manures and inorganic P fertilizer samples were also tested for comparison. This extraction is used by Pennsylvania in its official (inorganic) fertilizer testing program, and is commonly applied to other materials (due to its simplicity and broad acceptance as a P test method). For all materials tested, the NAC

Influence of load distribution and recycle rate in step-fed facultative ponds

This study presents the results of research on a wastewater treatment system with four identical facultative ponds in series with step-feeding and recirculation (SFFPR). Four modes of distribution of the influent were studied, which were (in percentages of the inflow per pond): C1 = 25/25/25/25; C2 = 50/20/20/10; C3 = 50/50/0/0; C4 = 100/0/0/0. The organic loading applied to the four ponds overall was around 200 kg BOD5/ha.d. The distribution C4 = 100/0/0/0 was selected for studying the recycle rate. Three recycling rates were studied: 0.5Q, 1Q and 2Q. COD and BOD5 removal efficiencies were high whatever the step-feed distribution. For the distribution C1 and C2, the four ponds were homogeneous. The equal distribution of organic loading rate in C2 distribution was most beneficial for algal growth. For piston pattern distributions (C3 and C4), the ponds receiving the highest loading showed a bacterial biomass higher than that of the primary production. Increasing the recirculation rate seemed to lead towards homogenisation of the ponds, while a decrease appeared to lead to their individualisation and increased their productivity. The SFFPR constitutes a stage of the treatment process which can replace the facultative stage; it produces a high effluent quality and decreases land area requirements.

Cultivating the increasingly popular medicinal plant, goldenseal: Review and update

AbstractInterest in the cultivation of goldenseal is increasing and this may have benefits for agriculture, human health, and conservation. To enable a better understanding of growing conditions, cultivation methods reported in the literature were reviewed, 21 natural goldenseal populations in the northern portion of its natural range in North America were described and analyzed in terms of population size and health, and 15 successful growers were interviewed on requirements for optimal cultivation. Growing conditions in the wild were compared to those reported in the cultivation literature. Summary of data from natural populations suggests goldenseal grows best in mixed hardwood forests, under 60–65% shade, in moist sandy loam soils high in organic matter, with pH 5.7 to 6.3. Similarly, review of the literature suggests that goldenseal grows best in moist, well-drained loams high in organic matter, with pH 5.5 to 6.5. Reported shade requirements vary but 47–80% shade is considered optimal. Growing conditions reported by growers were also consistent with the cultivation literature and similar to conditions of wild populations. Although optimal growing conditions are similar to those for many crops, goldenseal is relatively robust and can grow well in a variety of conditions including wet, predominantly sandy or clay soils with pH as low as 4.8 and as high as 7.8. Cultivation can utilize a ginseng crop infrastructure and goldenseal has been recommended as a rotation crop for ginseng. Commercial production of goldenseal is potentially advantageous because (1) it is an environmentally friendly crop; (2) it has been grown successfully far outside its natural range, is easy to grow, and is considered potentially profitable; and (3) it is relatively inexpensive, having low energy, land area, and fertilization requirements. Development of a sustainable crop may contribute to the protection of native wild germplasm, which can provide valuable material for crop improvement.

Anoxic ponds in the sugar cane industry: a case study from Colombia

Waste stabilisation ponds are a common technology used to treat sugar mill wastewaters in Colombia. Despite this there are problems related to biological process design and construction of these units. The situation with regards to operation and maintenance is far from satisfactory and also contributes to pond malfunctioning. In this sense, a pond system located at Providencia sugar mill on the southwest region of Colombia, South America was evaluated. The system comprises an anaerobic pond followed by a secondary anoxic pond. The whole system removes 73-82% of the BOD, with 53-70% occurring in the secondary anoxic pond, which is satisfactory despite the predominant conditions of organic overloading. However, TSS removal was low in comparison to BOD removal. The secondary anoxic pond proved to be an efficient treatment unit with the advantage of controlling odour release through photosynthetic bacterial activity. Land area requirements were less than those for green algal facultative ponds.