Grantee Research Project Results

Six sampling points (not identified in Figure 1) were positioned sequentially in the treatment train, identified as SP1 through SP6.  SP1 is the sampling from the inlet. Then, water during is sampled during treatment beginning with Fe-electrolysis (SP2), coagulation and flocculation (SP3), gravitational settling (SP4), rapid sand filtration (SP5) followed by an additional filtration step with a pleated micron filter (SP6).

A peristaltic pump dosed alum solution as a coagulant prior to the in-line static mixer, achieving 15 ppm aluminum in the water after mixing. Water quality parameters (pH, dissolved oxygen, conductivity, and turbidity) and bulk-solution parameters (total iron production, arsenic concentration) were monitored at the various stages of treatment to understand the system performance and particle removal (via monitoring turbidity). 

The pilot plant was operated for a total of 114 hours over a four month period and treated ~68,000 L of raw groundwater. Measured groundwater chemical concentrations are shown in Table 1.  There are no remarkable outliers other than the very high level of arsenic (bottom row in Table 1).  This value is very high compared to values in the GAMA database, but we were told by local community leaders that it is not unusually high for the local region. Additionally, the water had a very high TDS from the start, and this did not change much from our treatment, as expected.

Table 1: Concentrations of relevant groundwater species in Allensworth raw groundwater

The arsenic-removal performance of the drinking water treatment plant is summarized in Figure 2, over the period of the study (May to November 2022).

Figure 2: concentration of total arsenic (dissolved plus any attached to fine particulate matter) remaining in the finished processed water as a function of time.  Average arsenic concentration in the inlet water was 252 ppb, final (at exit) it was 1.2 ppb.

The range of turbidity, pH, conductivity, and dissolved oxygen are graphically represented in Figures 3-6 for the four month period of the pilot study.

Figure 3, showing turbidity at six sampling points (locations defined earlier, and again below). Figures 4, 5, and 6, chemical properties of water against operating hours.

The average total iron (Fe, dissolved plus particulate) concentrations in the water at various sampling points along the treatment are:

SP1      (inlet water)                                        0.1 ± 0.3 mg/L Fe

SP2      (post Fe-electrolysis)                          84.3 ± 21 mg/L Fe

SP3      (post coagulation and flocculation)    73.5 ± 43. mg/L Fe

SP4      (post gravitational settling)                7.0 ± 6.5 mg/L Fe

SP5      (post rapid sand filtration)                  6.7 ± 11. mg/L Fe

SP6      (post pleated micron filter)                 0.2 ± 0.7 mg/L Fe 

The post-electrolysis (SP2) Fe value is consistent with the expected total iron concentration of 86.8 mg/L Fe according to Faraday's law.  The treatment system consistently delivered treated water in which concentrations of relevant added ions (such as Fe and Al), and the turbidity, are below their allowable limits for drinking water; however, conductivity always remained above the  Secondary MCL for TDS as shown in Figure 4.

The plant operated as Zero Liquid Discharge. More than 99% of arsenic in the inlet water was captured and removed, attached to solid (moist) sludge, primarily comprising precipitated Fe(III) hydroxide.  This sludge was handled and disposed of per a plan for its safe management: it was transported and disposed of (meeting the EPA and State of California guidelines) appropriately in the UC Berkeley laboratory hazardous chemicals-waste stream. About four months of operation of this 600 LPH treatment plant in the field has provided strong evidence to support that ACAIE can continuously and effectively supply arsenic-safe water, starting with groundwater even of high initial arsenic concentration of 250 ppb.

Objective 2: Install sensors enabled for data collection and remote monitoring

The ACAIE field-test plant was equipped with sensors to continuously monitor operating parameters and the quality of treated water. Environmental sensors and electrical monitors were installed at the inlet and outlet of the ACAIE field-test plant to track water quality changes and critical operating parameters, ensuring effective arsenic removal.

In-line sensor modules and inexpensive microcontrollers (Arduino and Raspberry Pi) were programmed to enable remote monitoring of performance, and automate ACAIE plant functions, although throughout the reported experiment-period the treatment system was fully attended.

The envisioned (future) automatic control and monitoring system includes three components:

1. Hardware: Arduinos connected to a framework with a real-time cloud database and sensors (Atlas Scientific) were programmed to send data such as pH, dissolved oxygen (DO), conductivity, and turbidity to an online cloud-based data management platform. Operating voltage and resistance data was collected through power supplies.
2. Programmable System Controls and Dynamics: Real-time data collection allowed for system adjustments for optimal performance. For instance, if an impending overflow of a tank is detected, pumps and valves can automatically close to prevent spills or other issues.
3. User Application (in development): This still-in-development application will notify users of operational issues and provide treatment history, provide transparent data monitoring, and remote system operability. It will include a maintenance guide for community leaders and offer optional educational resources to raise awareness about water contamination.

Using inexpensive sensors and microcontrollers with control models substantially reduces the capital-outlay, without compromising the functionality and maintainability of the decentralized water treatment, keeping it affordable for low-income target communities. Items 2 and 3 reflect additional future work beyond the scope of this grant.

Objective 3: Conduct high resolution cost analysis of ACAIE community-scale plant

To assess the economic feasibility of our process, we conducted a comprehensive cost analysis over the operational period of the community-scale plant. This period includes the phases of construction, planning, purchasing, and two months of operation. Our economic evaluation considers two primary factors: capital expenditures and operating expenditures (both fixed and variable).

Total capital expenditures consists of the Inside Battery Limit (ISBL), Outside Battery Limit (OSBL), engineering and construction (E&C), contingency, and working capital (WC) costs. ISBL and OSBL and commonly used terms in engineering cost estimation.  ISBL costs cover all the equipment “inside the fenceline” in our system, and is detailed in the Equipment List in Appendix A, at 2021-2022 prices. These costs reflect the “catalog values” for purchasing the equipment. The total ISBL cost is the sum of these installed costs plus the uninstalled costs of any required spares. OSBL costs encompass related civil work and infrastructure outside the fenceline (such as upgrades to electrical and water supply, waste disposal processes, fire safety, equipment for the physical security of the plant, access roads, etc).  Furthermore, costs that would be clubbed under E&C, contingency, and WC were excluded from this financial analysis for the following reasons.  (1) UC Berkeley performed the engineering design work from funded resources whose value is not accounted for. (2) Allensworth community contributed voluntary labor to some of the construction work. (3) No working capital was needed. (4) No contingency funds were allowed. 

Furthermore, we have only estimated below the cost of financial management and oversight, physical purchasing of equipment and supplies, control of expenditures against invoices, and the cost of project management and oversight. These charges are not separately identified so it is not possible to extract exact numbers.  However, UC Berkeley’s overhead rate of 60% on all costs provides an estimate.  Although large mature organizations have higher efficiency in performing routine work, we have used that estimate below. Before management overheads, the total capital expenditure was calculated at $28.5 thousand (at 2021-2022 prices), as detailed in Table 2.

Table 2: Direct Capital Expenditure before overhead

Adding the 60% overhead (for management and support functions) for a large mature non-profit organization (in this case UC Berkeley) increases that estimate to $ 45,600.

The annualized capital cost of the ACAIE plant assuming a 10-year lifespan and 5% interest is therefore $5,804.

Our annual operating costs include both fixed and variable operating costs. Fixed costs typically cover expenses like rent, labor, insurance, land, permitting, and overall maintenance. However, for this project, land was provided by our community partners at no cost, and no rent was incurred. Maintenance and operational tasks were performed by UC Berkeley engineers, so those labor costs were not included in this analysis. As a result, the total fixed operating costs for the year are considered negligible.  These costs are also location-specific, and will need to be added based on where the water-treatment plant is located. We have excluded here all costs related to rent, operator-labor, land, permitting, and routine quality-control, testing, equipment calibration, and maintenance.

Variable operating expenses include consumables such as iron anodes and air cathodes for the ACAIE reactor, electricity usage, and aluminum sulfate used in the flocculation process. These variable costs for one year total $5.75 thousand, as shown in Table 3.

Table 3: Direct Variable Operating Costs

These costs too require management and support functions (e.g., invoices to be paid, control of expenses, accounting, placing orders for and receiving consumables). Therefore they too are subject to a reasonable overhead of 60%. Thus these annual variable costs increase to $9,200.

The air cathodes’ operating life is a key contributor to the overall cost of running the arsenic removal plant, as seen in Table 3. Extending air-cathode life reduces labor and operating costs. Soaking degraded air-cathodes for 16 hours in a 1% ascorbic acid solution can approximately double their lifespan, restoring performance close to that of new electrodes. In the above estimate this extended life for the air-cathodes is taken into account.

For a small town like Allensworth (population 600), we assume consumption of 4 Liters per person per day, i.e., a total of 2400 Liters per day.  Thus this requires use of the (600 LpH) pilot plant for 4 hours per day. It produces 864 KiloLiters of water per year.  Using this in the denominator, and the annual costs in the numerator, the cost per liter is ($5804+$9200)/864 KiloLiters = $0.017/L, or about 2 Cents per Liter.  Please see the caveats noted earlier that this number does not include the costs related to rent, operator-labor, land, permitting, and routine quality-control, testing, equipment calibration, and maintenance. Additional costs of marketing, public education to ensure water purchases, sales efforts, interest on borrowed Working Capital, and a business margin for investors in a for-profit enterprise must also be added, if this is operated as a business.